Well by now you likely know how brutal it is to be born in a livebearer community tank. If you want to let nature do the natual thing then just let them be and see what happens. If not, fish them out and into a breeder net or another container of water that you can heat and keep air in. I say container because I have seen people do some very resourceful things to save fry. I suggest keeping an extra 10gal handy for just such an occasion.
Once you can seperate them from the rest of the fish, feed them finely ground flake food until you can hatch some brine shrimp. Again having some brine shrimp eggs, airline rock salt, a shrimp net or coffee filter and a jar come in handy. Feed the fry small potions evry few hours when you are home. You let them gourge on brine shrimp and their guts are empty in 45 min. In nature, that is a good days feed, but your goal is to out pace nature and get them into the community tank ASAP! If you use a seprate container, a piece of airline makes a good siphon for daily water changes of 5% or so.