IVe found that using live foods for the baby fry as they grow, give off slightly larger guppies, and more vibrant colors. I Breed the indigo blue, Blue dragons.
currently feeding micro worms, baby brine shrimp and quality flake food. I’ve tried feeding them blood worms many times but they are repelled by them
even the adult guppies will go for these foods.
Also as stated lots of bidding places such as java moss, guppy grass, and so forth is important so the young are not eaten by the parents
Personally I keep males and females separate and fry go into their own grow out tank, but can be placed back into adult tanks once they are large enough.