The Causal Effect of Parent–Child Interactions on Child Language Development at 3 and 4 Years

Background: Language development is critical for children's life chances. Promoting parent–child interactions is suggested as one mechanism to support language development in the early years. However, limited evidence exists for a causal effect of parent–child interactions on children's language development. Methods: Data from the Language in Little Ones study, an Australian prospective birth cohort study (n = 296), was used to determine the sustained effect of parent–child interactions over time on children's language development at 36 and 48 months, measured using the Clinical Evaluation of Language Fundamentals Preschool-2 (CELF-P2) language assessment. Marginal structural models and inverse probability of treatment weights were used to allow observational data to emulate a randomised controlled trial by accounting for time-varying exposures and confounding. These results were then used to estimate the effect of several hypothetical scenarios where the exposure was fixed for the whole population at different levels (5th, 25th, 50th, 75th and 95th percentile) across the observed distribution of parent–child interactions. Results: Findings supported a causal effect of parent–child interactions from 6 to 36 (or 48) months on children's language development at 36 and 48 months, in a population of children without language impairment. The counterfactual language score at 48 months increased from 97.21 (95% CI 96.86, 97.56) for the scenario fixed at the 5th percentile to 102.15 (95% CI 101.80, 102.50) at the 50th percentile and 111.41 (95% CI 111.06, 111.76) at the 95th percentile. Conclusions: Although the effects of parent–child interactions on later language were small they do offer one mechanism to support early language development. These findings are discussed within the context of existing interventions to highlight the value of investment into sustained, universal prevention efforts for supporting early language. WHAT THIS PAPER ADDS: What is already known on the subject Promoting parent–child interactions within the home environment has been previously suggested as one mechanism to support children's early language development. Nonetheless, there is a lack of causal evidence and long-term follow-up to support this claim. What this paper adds to the existing knowledge The effect of parent–child interactions throughout the early years on children's language development is explored using causal inference methodology within an Australian prospective birth cohort study. Findings show a small causal effect of increasing parent–child interactions on children's language development at 36 and 48 months, after controlling for time-varying exposures and confounders. What are the potential or actual clinical implications of this work? This highlights the value of sustained, universal early intervention, which encourages back-and-forth parent–child interactions, as early as possible. Practitioners who work with parents and carers in the first year of a child's life should promote the importance of talking and interacting with their child to improve later language outcomes.