Betsy Hart addresses this issue in an article very much worth reading and pondering: Why send young away during church services? Here's Hart:
[T]he belief seems to be that it’s more likely kids will stick with church over their lifetime if it’s more geared to them when they are young. But the evidence is that this isn’t what happens.
Two decades ago, Christian education expert James W. Write showed in his book, Intergenerational Religious Education (Religious Education Press), that studies reveal that children who worship regularly with their parents are more likely to consistently worship as adults than children who grow up primarily attending “children’s church.”
I have not infrequently wondered whether the lower rate of church attendance in this country relative to that in the US might have something to do with breaking up families on sunday mornings rather than keeping them together, which is the pattern I grew up with. There is undoubtedly more than one causal factor at work here, but keeping our older children in church with us has to be a step in the right direction.