Kids and Maths and a cute joke

From Ellen and Robert Kaplan, founders of "math circles", a charming
anecdote:

"Take the counting numbers, which go on past any number of particles in the
universe, past any span of time you can conceive of," Robert Kaplan says.
"Is there a last counting number? In our math circle, it is a question that
I will ask of our class of six and seven-year olds: 'Is there a last
counting number?' Once a little girl said: 'Yes.' I said: 'Good, what is
it?' She said: '23,000.' 'Ah,' said I. 'Hmm.' A little boy said: 'What about
23,001?' And she said: 'Well, I was close.' "

More about the Math Circles (or Maths Circles in the UK) here.
Books by Robert and Ellen Kaplan : The Art of the Infinite: Our Lost Language of Numbers and The Nothing That Is: A Natural History of Zero.