If the freethinking parents are idiots then their children might see that and conclude that religion might be worth consideration.
Im my case I have 3 daughters all in their mid 20s now. Religion was never discussed in any great depth and they were never exposed to any significant religious influences. They simply grew up without religion. What are their attitudes now? Life is fine without religion, it just isn't an issue. In May my eldest (27) was married in Golden Gate Park, very formal, (e.g. I had to wear a Tux), but it was a very beautiful non-religious service, with vows said and exchanged, etc.
Now will they ever turn to religion at some point in their lives? I have no idea. If they do then fine, let them explore it. I have learnt so many tiems that trying to teach children that some things don't work so don't do it, just doesn't work very well. It is only now that when they try things that don't work I have the pleasure of them telling me, "I remember what you said". Haha, people on the whole need to experience for themselves to discover what works and does not.