Objective To investigate whether the total amount of time in childcare through the first 3 years of life was associated with children's receptive vocabulary, externalising and internalising problem behaviours at age 4–5 years, and whether this association varied for different types of childcare.

Methods We used data from the prospective, population-based Longitudinal Study of Australian Children (n=3208–4066, depending on outcome). Parental reports of the time spent in different types of childcare were collected at face-to-face interviews at age 0–1years and at age 2–3 years. Children's receptive vocabulary was directly assessed in the child's home, and externalising and internalising behaviours were measured by questionnaire, completed by parents and teachers at age 4–5 years.

Results At 3 years of age, 75% of the sample spent regular time in the care of someone other than the parent. After adjustment, more time in childcare was not associated with children's receptive vocabulary ability but was associated with higher levels of parent-reported (β=0.10 (95% CI 0.00 to 0.21)) and teacher-reported (β=0.31 (0.19 to 0.44)) externalising problem behaviours and lower levels of parent-reported internalising problem behaviours (β=−0.08 (−0.15 to −0.00)). Compared with children who did not attend any type of childcare, children in centre-based care had higher parent-reported and teacher-reported externalising and lower internalising problem behaviours.

Conclusions More time in centre-based childcare (but not other types of care) through the first 3 years of life was associated with higher parent-reported and teacher-reported externalising problem behaviours, and lower parent-reported internalising problem behaviours but not with children's receptive vocabulary ability at school entry.