I became SuperMommy when my son was two.
We were watching Sesame Street. (Actually, Sam was watching Sesame Street and i was working on the computer.) Super Grover came on and Sam got up, ran to his room, and came back with one of his old receiving blankets and told me he wanted to be Super Sammy. So I made a cape for him.
He then decided that i was no longer just plain ol' Mommy...he ran back to his room and grabbed another blanket, handed it to me, and said, "Here! You be SuperMommy!"
And so SuperMommy was born!