The food chosen to be best by most guppy breeders is brine shrimp. Most breeders recommend feeding baby brine shrimp to new born guppies and then larger brine as the fish grows until they are 4 months of age.

Preparing brine shrimp can be a chore though and guppies will eat a large variety of other foods as well. Guppies will eat small fry (their own and other fish's) as well as small worms or insect larva.

Any tropical fish food is good for guppies as well. It should be finely crushed into nearly a powder and fed in small amounts several times a day. Baby guppies are large enough to eat powdered flake food so this should not be a problem.

Having a tank with live plants in it as well will provide a home for small microorganisms to live, which will become food for any baby guppies which are born.