TV Quote from The Simpsons 03x18: Separate Vocations

Marge: Bart's grades are up a little this term, but Lisa's are way down.
Homer: We always have one good kid and one lousy kid. Why can't both our kids be good?
Marge: We have three kids, Homer.
Homer: Marge, the dog doesn't count as a kid!
Marge: No, Maggie.