This Will Easier to Explain with a Cone and Two Scoops

Nanny to five-year-old: Look, Stephen, there's a kitty!
Stephen, petting cat: Since boys have short hair and girls have long hair, then this kitty is a boy.
Nanny: Maybe not. Boys can have long hair and girls can have short hair too.
Stephen: Then how do you tell if it's a girl or a boy?
Nanny: How 'bout some ice cream?

Washington, DC