Me: Mom, can I have some makeup?
Mom: No. You are beautiful just the way you are.
Me: So that’s why you wear makeup?
Listen up, buttercup. The joke is that the kid asks for makeup, and the mom says she doesn't need it because she's already beautiful. But then the kid hits her with the zinger: "If I'm so beautiful, why do *you* wear makeup?" It's funny because it implies the mom doesn't think she's beautiful without makeup. Which is why your mom also wears makeup! Based.