The Boy was playing wizard. In his version, once a magic spell was cast, the last word anyone said (before the spell's completion) was what they turned into.

The Boy: Abracadabra, kalamazog. I turn you into a frog.

Justin: Poof!

The Boy: DAD! You said "poof!" Now you are a poof!

Me: Not that I've noticed.

Insert snickering like grade school children by the grownups.