After his bath tonight:
E: My towel has a hole in it!
Mommy: That's because it's been washed many times and we've been using the towel since you were 1 year old.
E: How old is it?
Mommy: Well, if you are almost 4 and we've been using it since you were 1...if you have 4 and you take away 1, what do you have?
E: (silence)
Mommy: What's 4 minus 1?
E: 4 is broken!
I guess we'll save math for another day...