I've been reading C.S. Lewis's The Abolition of Man, which is a rather interesting (though very short) book about education and teaching ethical systems. The discussion reminded me of how many people lead a life of practical atheism, and while virtuous, are unable to account for their virtue. It doesn't pose them any great problem in ordinary life, because in ordinary life people are not often called on to justify their virtue. Ordinary life for people who are not parents, that is.
Children are very interesting creatures, especially so because most children are philosophers. It's natural enough, since philosophy is the most practical way to start any task — when you need to go somewhere, your best bet is to start by asking where you're doing. If you've spent much time around people are about 4-5 years old (my memory is a little foggy on this point, so it might be 3-4 or 5-6), you'll find that they love to ask questions. Indeed, there's a common child's game which consists of asking "why?" to every answer an adult gives. Adult philosophers love this game too, but no adults will play it with them because they all know that the philosopher has better answers than they do. Children cannot be dismissed so easily because they really want to know.
And this is why, I suspect, so many people become religious when they have children. The series of questions have to end somewhere, and the only options are "because I said so", "because God said so", and "I don't know". There are a multitude of reasons why "because I said so" isn't a satisfactory answer, and "I don't know" is unsettling. People are homo sapiens, the wise man. It's hard to escape the feeling that they should know.
So that makes sense as one reason why people eventually often eventually return to their religion — having children brings people up against how inadaquate their non-philosophy is.
That does make for unfortunate implications for the growing trend of childlessness.