"When I was a child, I spoke like a child, I thought like a child, I reasoned like a child. When I became a man, I gave up childish ways." - I Corinthians 13:11
I Used to Believe
This is a great site with things that people used to believe as children. For example: "I believed Purgatory was like a doctor's office waiting room, only much bigger. It was filled with chairs and magazines to read while you waited to get into heaven."