Linguistic input is tuned to children's developmental level.

Children rapidly learn a tremendous amount about language despite limitations imposed on them by their developing cognitive abilities. One possible explanation for this rapid learning is that caregivers tune the language they produce to these limitations, titrating the complexity of their speech to developmentally-appropriate levels. We test this hypothesis in a large-scale corpus analysis, measuring the contingency between parents’ and children’s speech over the first 5 years. Our results support the linguistic tuning hypothesis, showing a high degree of mostly parent-led coordination early in development that decreases as children become more proficient language learners and users.