Infinity

4 y/o: Infinity doesn't exist.
Me: It does. But we can never count to infinity.
4 y/o: I can count to infinity!
Me: Can you?
4 y/o: Yes. Infinity comes after 1,038. (Sadly, realising he can't count to infinity after all.) But I can't count to 1,038.
(4 y/o goes back to playing football in the house, which he's been asked repeatedly to not do.)
4 y/o: GOOOOOOOOOOOOOOAALLLLLLLLL!!!