A decade of ManyBabies research, testing thousands of babies across hundreds of labs, has shown that some, but not all findings in infant research replicate well. Collectively, these projects have shown us that our methods carry limitations that larger samples alone cannot resolve. Here we present three lessons that point toward a more reliable, inclusive developmental science.

Though a wealth of research has found that young infants have the capacity to evaluate helping and hindering agents (e.g. Hamlin, 2007; for a review, see Woo et al., 2025), it is nevertheless unclear whether these evaluations reflect mere social evaluations or more mature understanding of moral concepts. The present experiments probed the nature of infants’ evaluations by testing whether they associate the morally-relevant words “good” and “bad” with helpers and hinderers. In Exp.1, 32 19-month-olds watched a live puppet show where a protagonist puppet is either helped or hindered by another puppet (ball show, adapted from Hamlin & Wynn, 2011). Then, the infant was presented with the helper and hinderer puppets, and asked, “can you point to the good/bad guy?”. Results revealed that whereas infants reliably mapped “bad” to the hinderer (24/31, p = .003), they showed relatively inconsistent mapping of the word “good” to the helper (p = .09). In Exp.2, 42 20-month-olds watched a video recording of the ball show, then engaged in a preferential looking paradigm in which still images of the helper and hinderer were shown on the screen. An audio prompt then asked, “Where’s the good/bad guy? Find the good/bad guy,” while an eye-tracker monitored infants’ gaze. Results paralleled and bolstered that of Exp.1: infants looked significantly longer at the hinderer when hearing the “bad” prompt, but looked equally at both characters when hearing the “good” prompt. Together, these findings suggest that infants may associate the abstract moral word “bad” with hindering behaviour prior to the second birthday, but the association between “good” and helping behaviour may emerge later. This asymmetry provides further evidence for a negativity bias in social cognition.

Thomas suggests that evidence suggestive of an innate moral core can instead be explained by relationship inferences and evaluations. We argue that the analogy between other demonstrations of prosociality (e.g., helping) and imitation is insufficient, and additionally highlight key findings that appear inconsistent with a relationship-centric view of infants' sociomoral capacities.

A decade of ManyBabies research, testing thousands of babies across hundreds of labs, has shown that some, but not all findings in infant research replicate well. Collectively, these projects have shown us that our methods carry limitations that larger samples alone cannot resolve. Here we present three lessons that point toward a more reliable, inclusive developmental science.

Do toddlers and adults engage in spontaneous Theory of Mind? This multi-lab collaboration examined whether 18- to 27-month-olds’ and adults’ anticipatory looks distinguish between two basic forms of epistemic states: knowledge and ignorance. In adults (n = 703, 68% female), we found clear evidence that they do: they showed simple goal-based action anticipation in pilot studies and differentiated between knowledge and ignorance conditions in the main study. In toddlers (n = 521, 49% female), results were less conclusive. While demonstrating goal-based action anticipation in pilot studies, they did not differentiate between knowledge and ignorance as predicted. Future research can explore adults’ sensitivity to more complex epistemic states like true/false beliefs and clarify whether toddlers’ results reflect competence or performance limitations.

Evaluating others’ actions as praiseworthy or blameworthy is a fundamental aspect of human nature. A seminal study published in 2007 suggested that the ability to form social evaluations based on third-party interactions emerges within the first year of life, considerably earlier than previously thought (Hamlin, Wynn, & Bloom, 2007). In this study, infants demonstrated a preference for a character (i.e., a shape with eyes) who helped, over one who hindered, another character who tried but failed to climb a hill. This study sparked a new line of inquiry into infants’ social evaluations; however, numerous attempts to replicate the original findings yielded mixed results, with some reporting effects not reliably different from chance. These failed replications point to at least two possibilities: (1) the original study may have overestimated the true effect size of infants’ preference for helpers, or (2) key methodological or contextual differences from the original study may have compromised the replication attempts. Here we present a pre-registered, closely coordinated, multi-laboratory, standardized study aimed at replicating the helping/hindering finding using a well-controlled video version of the hill show. We intended to (1) provide a precise estimate of the true effect size of infants’ preference for helpers over hinderers, and (2) determine the degree to which infants’ preferences are based on social features of the Helper/Hinderer scenarios. XYZ labs participated in the study yielding a total sample size of XYZ infants between the ages of 5.5 and 10.5 months. Brief summary of results will be added after data collection.

The current article describes the Remote Infant Studies of Early Learning, a battery intended to provide robust looking time measures of cognitive development that can be administered remotely to inform our understanding of individual developmental trajectories in typical and atypical populations, particularly infant siblings of autistic children. This battery was developed to inform our understanding of early cognitive and language development in infants who will later receive a diagnosis of autism. Using tasks that have been successfully implemented in lab-based paradigms, we included assessments of attention, memory, prediction, word recognition, numeracy, multimodal processing, and social evaluation. This study reports results on the feasibility and validity of administration of this task battery in 55 infants who were recruited from the general population at age 6 months (n = 29; 14 female, 15 male) or 12 months (n = 26; 14 female, 12 male; 62% White, 13% Asian, 1% Black, 1% Pacific Islander, 22% more than one race; 6% Hispanic). Infant looking behavior was recorded during at-home administration of the battery on the family's home computer and automatically coded for attention to stimuli using iCatcher+, an open-access software that assesses infant gaze direction. Results indicate that while some tasks replicated lab-based findings (attention, memory, prediction, and numeracy), others did not (word recognition, multimodal processing, and social evaluation). These findings will inform efforts to refine the battery as we continue to develop a robust set of tasks to improve the understanding of early cognitive development at the individual level in general and clinical populations.

Humans establish and maintain complex cooperative interactions with unrelated individuals by exploiting various cognitive mechanisms, for instance empathic reactions and a preference for prosocial actions and individuals over antisocial ones. The key role played by these features across human sociomoral systems suggests that core processes underpinning them may be evolved adaptations. Initial evidence consistent with this view came from studies on preverbal infants, which found a preference for prosocial over antisocial individuals. In this study, 5-day-old neonates were shown pairs of looping video interactions in which a prosocial event (approach in Experiment 1, helping in Experiments 2 and 3) appeared on one side of the display and an antisocial event (avoidance in Experiment 1, hindering in Experiments 2 and 3) appeared on the other; newborns' attention to each event type was measured. Across 3 experiments, newborns consistently looked longer at the prosocial than the antisocial events, but only during socially interactive versions of the stimuli. Together, these findings suggest that basic mechanisms to distinguish simple prosocial versus antisocial acts, and to prefer prosocial ones, emerge with very limited experience.

From early on, infants show a preference for infant-directed speech (IDS) over adult-directed speech (ADS), and exposure to IDS has been correlated with language outcome measures such as vocabulary. The present multi-laboratory study explores this issue by investigating whether there is a link between early preference for IDS and later vocabulary size. Infants' preference for IDS was tested as part of the ManyBabies 1 project, and follow-up CDI data were collected from a subsample of this dataset at 18 and 24 months. A total of 341 (18 months) and 327 (24 months) infants were tested across 21 laboratories. In neither preregistered analyses with North American and UK English, nor exploratory analyses with a larger sample did we find evidence for a relation between IDS preference and later vocabulary. We discuss implications of this finding in light of recent work suggesting that IDS preference measured in the laboratory has low test-retest reliability.

Test-retest reliability --- establishing that measurements remain consistent across multiple testing sessions --- is critical to measuring, understanding, and predicting individual differences in infant language development. However, previous attempts to establish measurement reliability in infant speech perception tasks are limited, and reliability of frequently-used infant measures is largely unknown. The current study investigated the test-retest reliability of infants' preference for infant-directed speech over adult-directed speech in a large sample (N=158) in the context of the ManyBabies1 collaborative research project (Frank et al., 2017; ManyBabies Consortium, 2020). Labs were asked to bring in participating infants for a second appointment retesting infants on their preference for infant-directed speech. This approach allowed us to estimate test-retest reliability across three different methods used to investigate preferential listening in infancy: the head-turn preference procedure, central fixation, and eye-tracking. Overall, we found no consistent evidence of test-retest reliability in measures of infants' speech preference (overall r=.09, 95% CI [-.06,.25]). While increasing the number of trials that infants needed to contribute for inclusion in the analysis revealed a numeric growth in test-retest reliability, it also considerably reduced the study's effective sample size. Therefore, future research on infant development should take into account that not all experimental measures may be appropriate for assessing individual differences between infants.

A growing literature suggests that preverbal infants are sensitive to sociomoral scenes and prefer prosocial agents over antisocial agents. It remains unclear, however, whether and how emotional processes are implicated in infants' responses to prosocial/antisocial actions. Although a recent study found that infants and toddlers showed more positive facial expressions after viewing helping (vs. hindering) events, these findings were based on naïve coder ratings of facial activity; furthermore, effect sizes were small. The current studies examined 18- and 24-month-old toddlers' real-time reactivity to helping and hindering interactions using three physiological measures of emotion-related processes. At 18 months, activity in facial musculature involved in smiling/frowning was explored via facial electromyography (EMG). At 24 months, stress (sweat) was explored via electrodermal activity (EDA). At both ages, arousal was explored via pupillometry. Behaviorally, infants showed no preferences for the helper over the hinderer across age groups. EMG analyses revealed that 18-month-olds showed higher corrugator activity (more frowning) during hindering (vs. helping) actions, followed by lower corrugator activity (less frowning) after hindering (vs. helping) actions finished. These findings suggest that antisocial actions elicited negativity, perhaps followed by brief disengagement. EDA analyses revealed no significant event-related differences. Pupillometry analyses revealed that both 18- and 24-month-olds' pupils were smaller after viewing hindering (vs. helping), replicating recent evidence with 5-month-olds and suggesting that toddlers also show less arousal following hindering than following helping. Together, these results provide new evidence with respect to whether and how arousal/affective processes are involved when infants process sociomoral scenarios.

Young children often encounter unsolvable problems with which they require others' help. To receive adequate assistance, children must be savvy about whom they seek help from: Effective helpers must possess both the ability to help (e.g., competence) and a willingness to do so (e.g., benevolence). Although past work suggests that information about competence and benevolence can inform young children's help-seeking behavior, it remains unclear how and whether children utilize said factors independently of each other. Furthermore, it is unclear whether they can generalize potential helpers' competence from one task to another. The current experiments examined whether 22- to 23-month-olds confronted with a broken toy selectively sought help from agents who had previously demonstrated either competence (Experiment 1) or benevolence (Experiment 2). In Experiment 1, infants preferred to seek help from a competent agent who successfully opened a closed box over one who failed to do so. In Experiment 2, infants selectively sought help from a benevolent agent who helped a third party by returning a lost ball, over an agent who stole the ball instead. These patterns of selectivity were not driven by associative valence matching; in Experiment 3, infants showed no preference for an agent who was itself helped versus an agent who was hindered. These results suggest that before their second birthday, infants independently utilize cues to both competence and benevolence to inform their help seeking, using information generalized from novel contexts. We discuss the potential nature of this generalization as well as directions for future work.

From their observations of others’ behavior, adults quickly form character impressions. These impressions can be “sticky”, such that adults prioritize information acquired earlier over later information. Developmental psychology has provided some evidence that infants, like adults, may form impressions based on others’ prosocial and antisocial behavior. But how do infants respond to inconsistent behavior? Do infants update their impressions when people behave inconsistently? The present, preregistered experiments examined 11-month-olds’ (N = 189) ability to incorporate inconsistency in their social evaluations. We first successfully replicated the finding that when actors behave consistently, infants prefer looking to helpers over hinderers (Experiment 1). In our key experiments, infants observed an actor who behaved inconsistently (either mostly helping or mostly hindering) paired with an actor who behaved consistently (either always hindering or always helping, respectively). Would infants prefer the actor who was on average more prosocial? We found that infants preferred looking to more prosocial actors, but they did not look longer when an actor’s behavior changed, suggestive that they did not notice the change in behavior. Finally, in Experiment 3, we found that infants’ evaluations of inconsistent actors in Experiment 2 may be due to a primacy bias: a focus on what an actor did first, rather than an ability to incorporate consistency. Together, these findings raise the possibility that infants’ social evaluations are based on their first impressions of others. These findings may reflect a developmental precursor to adults’ “sticky” character impressions.

Spelke's What Babies Know masterfully describes infants' impressive repertoire of core cognitive concepts, from which the suite of human knowledge is eventually built. The current commentary argues for the existence of a core concept that Spelke claims preverbal infants lack: social goal. Core social goal concepts, operative extremely early in human development, underlie infants' basic abilities to interpret and evaluate entities within the moral world; such abilities support claims for a core moral domain.

Can well-documented gender differences in evaluations of prosocial versus antisocial actions found in childhood and adulthood be traced to sex differences in basic sociomoral preferences in infancy? We provide an answer to this question by meta-analyzing sex differences in preference for prosocial over antisocial agents in a set of 53 samples of American and European infants and toddlers aged between 4 and 32 months (N = 1,094). Although the original studies were agnostic to sex differences, we were able to retrieve the original data sets and estimate the effect of infants' and toddlers' sex on sociomoral preferences. Employing both a standard frequentist and a Bayesian approach to meta-analysis, we found strong evidence supporting the absence of sex differences in sociomoral preferences among infants and toddlers. We discuss the relevance of this finding for theories and descriptions of the emergence and developmental trajectory of gender differences in morality. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Grossmann posits that heightened fearfulness in humans evolved to facilitate cooperative caregiving. We argue that three of his claims - that children express more fear than other apes, that they are uniquely responsive to fearful expressions, and that expression and perception of fear are linked with prosocial behaviors - are inconsistent with existing literature or require additional supporting evidence.