Clever reasoning

Yesterday while driving to friends' house to trick-or-treat, Lily said that molecules are the smallest thing in the world. I told her that there may be smaller pieces than molecules and scientists are still discovering smaller and smaller parts. She thought about this and then said "I think it must go on forever, because everything has to be made of SOMETHING, so the smallest thing is still made up of of smaller pieces and those pieces are made up of smaller pieces..."