Children are born with faith and unlimited hope. To a child, anything is possible. Most kids naturally believe there is a God, and most want to believe in miracles and Heaven and life after death.
The challenge comes when hopes are disappointed, people let one another down, and prayers are not answered the way we expect them to be. As children begin to grow up, they learn to doubt and question and seek tangible proof for truth.
Today, our schools even teach kids that truth is relative. In other words, you can invent your truth, and I can invent mine. (Does that make it true? According to many modern educators, it does.)
As children grow older and more educated, it becomes possible to teach them to doubt the existence of God. Is this a worthwhile pursuit? The educators are left to decide for themselves. Whoever holds the chalk can hold what they believe to be true.
Actually, it is nearly impossible to teach children about atheism. Sure, children may be taught about it IN THEORY, but they will never believe it.
Perhaps that is why Jesus said, "I tell you the truth, unless you change and become like little children, you will never enter the kingdom of heaven" (Matthew 18:3).