What we may find difficult to understand, children often know and accept instinctively.  This is often true of God.  Whereas children may find some elements of religion itself confusing, they will not usually struggle to understand God.  They are ready for meaningful information at a surprisingly young age.

A child will see through hypocrisy, so rather than send your children off to church and Sunday school to be taught by people you've never even met, why not take them?  Why not get involved in the local fellowship and get to know the believers who will be a part of your little one's spiritual education?

The same goes for prayer, if a child needs to learn to pray (and they do), then so do you as a mom or dad.  Pray with your children.  Let them see and hear you as you also open your own heart to God.

The most important lessons I ever received about God came from the things my mother told me when I was about 3 or 4 years old.  I have never forgotten her simple lessons and comments.  She did not know a lot about God, since she was not even a practicing believer at the time.  But she gave me her own honesty and she gave me the basics, which was all she had.  I thank God every day for those early and all-important lessons.