Until I was about 9 (my scoutmaster explained the truth to me) I thought the word "Amen" had something to do with the Trinity. A-(one) God in Three "men" (Father, Son, Holy Ghost). "Amen" was to be sure the prayer went to all three, I guess.
Also, I used to think that the phrase in the American Pledge of Allegiance "One nation under God, indivisible" was "...under God invisible" (since I had been taught that God is invisible). I think my scoutmaster cleared that up, too.
A childhood belief about prayers

others believed things like this
- I used to think that One nation, under god, indivisible was invisible— Aeris
- Yesterday I realised that invisible ink doesn`t make me invisible.— Jonathan Eleven years old
- I used to believe that the Holy Trinity was Dad, God and Santa Claus!— Cathy P.
- Through second grade I always concluded the pledge with '...indivisible, with liberty and just a straw.'— George
- "God is good, God is great, lettuce thank him for our food Amen"— pj
- there was a young girl i used to know that would say 'onion' at the end of grace, instead of 'amen'— matt