We have many discussions in our house about religion. DH is atheist and I am Catholic, we are raising our kids Catholic. But, they know daddy is not Catholic and that he believes different things than I do and that we want them to learn about my religion so that they can make an informed decision about whether or not they believe.
We have had to content with a Sunday school teacher telling DD (then 5) that people who don't believe in God are bad! She apparently had an argument with the woman about her daddy and friends who are not Catholic not being bad people.
We've also had discussions about how the big bang theory fits in with the idea of God creating the universe and everything in it. Someone had tried to tell her that she had to chose which one she believed to be true, and she wasn't/isn't willing to make that choice (not that I think she needs to either, but that is a different topic). This all led to the question "If God created everything, what created Him?"
So, I guess my point is, that it is really dependent on how firmly you believe you want your children to believe the same thing you do. We are very open with DDs and answer their questions very differently, but the main thing is that they are open to differences and accepting of them.