Which time investments in the first 5 years of life matter most for children's language and behavioural outcomes at school entry?

Background: The ways children spend their time is one of the most valuable inputs for healthy child development. It is unknown which time investment yields the greatest return for children's language and behavioural outcomes at school entry. Methods: We used data from the first three waves (2004, 2006, 2008) of the Longitudinal Study of Australian Children (n=4253). At every wave, parents completed 24-h time-use diaries on one randomly selected week and one weekend day. The amount of time children spent on 11 activities at ages 0-1, 2-3 and 4-5 years was analysed. Receptive vocabulary was assessed using the Peabody Picture Vocabulary Test, and externalizing behaviours were measured by the Strengths and Difficulties Questionnaire, completed by parents and teachers at 4-5years. To identify which time investment in the first 5 years of life mattered most for children's outcomes, a new production function was developed. This production function was estimated using a log-log linear regression model. Results: Relative to other time investments, time spent on educational activities at 2-3 years of age was the most important time investment for receptive vocabulary and behavioural outcomes at school entry. After adjusting for confounding, every 1 h invested in educational activities at 2-3years was associated with a 0.95% [95% CI (confidence interval): 0.62, 1.28] increase in receptive vocabulary, and a -5.72% (95% CI: -7.71, -3.73) and -9.23% (95% CI: -12.26, -6.20) reduction in parent- and teacher-reported externalizing problem behaviours. Time invested in play was also important to both receptive vocabulary and behaviour. One hour invested in play at 2-3 and 4-5years was associated with a 0.68% (95% CI: 0.38, 0.98) and 0.71% (95% CI: 0.39, 1.03) increase in children's receptive vocabulary at school entry. In addition, time invested in play at 2-3 and 4-5years was associated with reduced problem behaviours at school entry. In contrast, screen time at all ages was associated with poorer parent- and teacher-reported externalizing problem behaviours. Conclusions: These results suggest that time invested in educational activities at 2-3years of age yield the greatest return for children's receptive vocabulary and behaviour at school entry.