They stay small. Really small. You do not need to worry about their size because they won't likely get much bigger than when you got them, unless you got them really young.
ChilDawg, what do you consider small? Whatasave, you want to be more specific as to what small is. That would be helpful. They should get to about 7cm(2.8 inches). How big are they?
Good point, DarkAngel. I consider about 2-2.5" small (which is the length at which every LFS I've seen seems to sell them), because they just look small to me, but I guess I'm a tankbuster boy at heart. Whatasave, measurements would be necessary.