Well it depends if their is enough water through you hatchery, fry will happily feed in crushed flake food and will love small live foods.
fry should idearly be feed 3 times a day.
If their is little water flow you can get a quick build up of toxins, like ammonia which can kill then very quickly...
Once the fry have doubled their size their ok with other mollies but many other fish will still eat them, until the 1.5-2 cm