I'm not so sure I agree with your premise that children don't really understand about God at a young age. My son and his wife do not believe and yet when I mentioned God to my grandson, when he was only about four, I learned he had knowledge of God. I have no idea where he got it from because I know it wasn't from his parents.A child can be sanctified...I've taught our faith to children and I have witnessed this first-hand. However, it is highly unlikely because they don't really understand about God yet.
Now he is 10 and my beliefs are in stark contrast to my son's so my grandson is getting confused. This past week he spent three days at my house over MEA week. At one point after we prayed before our meal, he commented that he "chose to not believe" and I asked him why. He began to speak about how the universe was formed by molecules coming together to form higher substances and eventually planets and so forth. That was definitely his father, my son the scientist, speaking. I just calmly replied, "Where do you think all those molecules came from?"