Do you have one or two tanks? If you only have one tank, do you have a breeders trap? what are they fry doing ATM (i.e. have you separated them from the parents)..
The best thing to do ATM, is put the fry into a breeding trap/net in your tank...this way you can feed them as often as need be and with the foods they need to grow.
As for feeding....you need to feed many small feeding i.e. 4-5 a day with a baby food powder (available from your LFS)....if this is not available, take normal flakes and ground them up very fine then sprinkle it on the water....
Also, you need to keep the tank they are in very clean as bad water conditions can stunt their growth. The little guys also produce a LOT of waste.
Good luvk withthe little guys.....do you plan on keeping them all?