This was a conversation between my three-year-old son and I this evening. He was putting change into his "pikky pank" (translation: piggy bank) and didn't want me to help:
Ben: No Mommy, this change is only for kids!
Me: (Teasing him) Mommy's not a kid?
Ben: No, Mommy, you're a girl!
Me: Wait, Rachel and Julie are girls and they're kids, too, right? (Referring to his cousins)
Ben: No, they're only girls.
Me: Oh, so only boys are kids?
Ben: (matter-of-factly) Yep!