NOOO! If they're pond snails, get them out, now, before they take over!
I was like you...I though, oh, how cute, tiny little snails, I'll let them live in my tank...until I realized that the things are like gremlins and they propagate every ten seconds. I swear you start with one, and before you know it they've eaten an entire wisteria bunch and there are a thousand of them in there.
As for getting rid of them...they are ferocious little buggers. They even survive salt. I swear at the end of the world there will be twinkies, roaches, and pond snails. ;) You can either fish them out any time you see them (sometimes you can vacumn them up as well), put in a peice of: kale, lettuce, or sliced cucumber and remove them once they're latched onto there, or, and this is what has worked the best for me, buy a couple of assassin snails and let them do your dirty work for you.
They're cute and you feel bad for them at first...then they eat 30$ worth of plants and suddenly you don't feel quite so awful about disposing of them anymore. :(