When I was younger, I had issues with repeating the same thing over and over impulsively (usually something that never made sense). This one was my favourite:
"A man once went to kick a soccer ball, but he missed and he flew up into space and never came down!" (Yeah, that makes sense)
I also vaguely remember this conversation with my dad when I was really, really little:
"Dad, how come we can't see air?"
(He says something along the lines of 'because it's clear')
"Oh, but if we could see air, since it's everywhere, wouldn't that mean we couldn't see at all?"