The Pleco shouldn't, but they have been known to eat fish. You need to get a breeder net or something along the same lines. This seperates the fry from the rest of the fish so they are easier to feed and keep safe. Or, you could get a 5 gal
tank, seed the filter with media and gravel from your current tank, and raise them in there until they get larger.
I had mollies that reproduced like crazy, be prepared.