What things have you done or said that made children laugh (yours, or others)?
My niece howled with laughter at the way I read Thomas the Tank Engine in a "serious" voice. "The bucket was old, and it had five holes, so they had to lower it into the river, and empty it into Thomas's tank as quickly as they could."
I tend to say "stupid stupid!" in annoyance if I make a mistake. Again, this has caused a few young laughs: I think children are told never to call anybody "stupid" nowadays.