I think you're assuming that all children will automatically follow their parents' beliefs and be as much or more involved in that religion as they are, which is an incorrect assumption. That depends on the religious fervor of the parent.

And sometimes, it depends inversely: the more fervent the parent, the more the child spots that it's a bad idea. Not always, though.

Perhaps it's worth it for atheist parents to pretend to be very religious when their children are young, so that when the children automatically rebel against them, they'll end up doing the right thing...

Peter