Here is my improved version:
A certain number of ants go marching. When they start out, the number of ants is prime, so they decide to march one by one. After a while, the little one stops to suck her thumb, and the ants leave her behind. Now the number of ants marching is even, so the ants go marching two by two. Then one ant stops to tie his shoe, and the ants leave him behind. Now the number of ants is divisible by three, so the ants go marching three by three. Soon, one of the ants stops to climb a tree, and the ants leave her behind. Now the number of ants is divisible by four, so the ants go marching four by four. What is the fewest number possible of ants that originally went marching?
Details and Assumptions – There can't be a negative number of ants.