We sang a hymn/religious song (I think it was more modern than a hymn judging by the informal lyrics) at school with the line "who made Earth and Mars?" This always annoyed me because the Bible says God made Earth, but has no mention of the other planets. I had also learnt from science books that the planets were formed naturally with no influence from God. So whenever we sang the hymn, I wouldn't say the words "and Mars", because I knew God had nothing to do with making it.
A childhood belief about hymns

others believed things like this
- I used to believe God had a pet tortoise. There was a hymn we sang that went "Great things he hath taught us"— Lozza
- When he was a kid, my husband thought the hymn "bringing in the sheaves" was "bringing in the cheese."Anon
- I used to believe that the moon was another country and that all countries were little planets.Anon
- Billy Squire sang about "My Kind of Lover". My wife sang about "My Candelabra"— Wailerman
- I used to believe that other coutries were other planets and you had to travel in a spaceship to go to Africa.— Sarah Jane
- I believed dinosaurs made the mountains whenever they walked the earth.— Tammy