Introduction Disentangling the effects of maternal depression in toddlerhood from concurrent maternal depression on child behaviour is difficult from previous research. Childcare may modify any effects of maternal depression on subsequent child behaviour, but this has not been investigated widely.

Methods We examined the influence of maternal depressive symptoms during toddlerhood on children's behaviour at age 5½ years, and investigated if formal or informal childcare during toddlerhood modified any relationship observed.

Results Data were available from 438 mothers and their children (227 girls, 211 boys) who completed questionnaires during children's infancy, toddlerhood and at age 5½ years. Recurrent maternal depressive symptoms in toddlerhood was a significant risk factor for internalising, externalising and total behaviour problems when children were aged 5½ years. Formal childcare at age 2 years modified the effect of recurrent maternal depressive symptoms on total behaviour problems at child age 5½. Neither intermittent maternal depressive symptoms nor informal childcare in toddlerhood significantly affected child behaviour problems.

Conclusion Recurrent, but not intermittent, maternal depressive symptoms when children were toddlers had a longer term effect on child behaviour problems at child age 5½ years. As little as half a day in formal childcare at age 2 years significantly modified the effect of recurrent maternal depressive symptoms on total behaviour problems. Formal childcare for toddlers of depressed mothers is a pragmatic, supportive strategy that may have positive short and longer-term benefits for affected mothers and their children.