Nowadays many more young children experience non-maternal childcare than in the past. From a theoretical perspective, the effect this may have on their cognitive and behavioural development is unclear. This paper uses data from the UK for a sample of children in the Millennium Cohort Study, whose mothers were working when they were nine months old, to test how different forms of childcare at an early age play a role in the production of cognitive skills and the behavioural development of young children (measured at age three). The results show that formal group care is positively associated with school readiness test scores. But, unlike previous research, we find no association between formal group care and problem behaviour. Grandparent care, which has received negative attention in the past, is shown to be positively associated with vocabulary test scores, but also positively related to problem behavioural scores.