One,Two, Three, Infinity is probably the best possible introduction to math for kids. The big challenge is skipping ahead to the "cool stuff" for kids who are

One,Two, Three, Infinity is probably the best possible introduction to math for kids. The big challenge is skipping ahead to the "cool stuff" for kids who are still young enough to lack facility with algebra. Most attempts to do this are either hand-waving or unfairly advanced. But the real solution is to show them genuine math that doesn't require any solving for x, like Cantor's diagonalization lemma.