This study aimed to investigate the relationship between external childcare and child problem behaviour at age 7 in a culturally diverse urban sample from Switzerland. We used data from the Zurich Project on the Social Development of Children and Youths (z-proso). Findings suggested that the quantity of group-based childcare (but not individual childcare) was related to aggression, ADHD, non-aggressive externalizing behaviour, and anxiety and depression at age 7. Analyses on timing of childcare suggested that the accumulation of childcare over the life course, and not so much childcare in the first years of life, was associated with child problem behaviour. In addition, childcare at age 5 to 7 had a unique relationship with problem behaviour over and above quantity of group-based childcare received in other age periods.