Kids who start going to large child-care facilities before age two and a half tend to develop more colds and ear infections at that age, but they then catch fewer illnesses once they get to elementary school, new Canadian research finds.

Parents of kids at daycare centres know all too well that their children seem to get more colds and infections than kids who stay at home or who go to home-based daycares.

That's led some to worry about the effects of exposing kids to a wide range of pathogens at such a young age. But few studies have looked at how group child care affects sickness rates beyond the preschool years.

So Sylvana M. Côté, of Ste-Justine Hospital and the University of Montreal led a team who studied more than 1,200 Quebec families of newborns born in 1998.

They asked the mothers whether their children went to a large child-care facility (defined as a centre that cares for up to 10 groups of eight to 12 children; a small child-care facility (home-based centres where a caretaker watches three to eight children); or were cared for at home.

For eight years, the researchers regularly collected information about how often the children had colds and respiratory tract infections, ear infections or stomach infections.

They found that compared with kids cared for at home until elementary school, those who began going to a large group child care before age 2 ½ had higher rates of respiratory infections and ear infections during early preschool. But those children then had lower risks of respiratory tract or ear infections during early elementary school.

The children who started in small group child care in early preschool and never went to a large care setting did not have any differences in infections.

Those who were first cared for at home but then went to any size child care facility during late preschool had a higher risk of ear infections at that time, but no other differences in infection risk.

Interestingly, group child care was not associated with gastrointestinal infections at any period in the children's development, the authors report in Archives of Pediatrics & Adolescent Medicine.

The findings suggest that early exposure to large groups of children early in life gives kids some protection against infections they might encounter again in grade school.

The authors say their findings mean that parents can be assured that although their young children may contract a lot of infections after starting at a large group child care centre, the increase in infections is temporary, and is likely to provide the children with greater immunity during the elementary school years.

The authors write: "Children who initiate large-group child care early (i.e., before age 2 ½ years) may even gain protection against infections during the elementary school years, when absenteeism carries more important consequences for school adaptation and performance."

The authors add that their findings suggest that developmental processes may explain the link between early exposure to large groups of children and reduced infection risk.

"One possible mechanism that has received empirical support in the context of long-term protection against asthma involves an increased repeated stimulation of the immature immune system by early and mild infections," they write.

"Future studies are necessary to investigate this and other mechanisms that may account for the results."