The researchers said the results should reassure parents that a rise in infections experienced by their child is likely to be temporary and will provide them with greater protection later.
Canadian researchers led by Dr Sylvana Cote studied 1,238 families with a newborn living in Quebec in 1998. Parental reports were then taken of infections when their children were in elementary school (five to eight years old).
They found participation in large group child care before 30 months was associated with increased infections at that time, but that it protected against infections during the early school years.
Dr Cote and her team said their findings provided reassurance for parents about their choices of group size and age at enrolment in child care.
Over the course of eight years, such choices should not have a major effect on health, at least in terms of respiratory tract infections with fever and gastrointestinal and ear infections, the researchers said.
They added: 'Although children exposed to large group child care are likely to experience an increased frequency of infections compared with children cared for at home, this increase should be limited to the period around enrolment into group child care.'
The researchers concluded: 'Physicians may reassure parents whose children initiate large group child care early that their child's experiencing of infections is temporary and is likely to provide them with greater immunity during the elementary school years.'