Baby goldfish means, how small?
If they are about an inch or two in size, you should feed them a varied diet with two good-quality staple foods (preferably small pellets or flakes), along with some freeze-dried live foods, like bloodworms, krill, tubifex... they need the protein to grow big and healthy!
Some peas are also good (: Buy some frozen peas (without salt), thaw them and pop them out of their shells. You'll probably also have to cut them into smaller pieces for your babies to eat!

Otherwise, you should just keep an eye on the water quality, and make sure that the water is fresh, by doing weekly water changes That's about it (: Good luck with your new fish!

Brine shrimp nauplii are wonderful to feed baby goldfish, newly hatched, since they swim around in the tank and they stay alive for a while so everyone can get their food! Another thing that's good to do with the tank where the goldfish fry reside would be to grow algae on the sides, very good food for them (: And they can graze on it to their hearts' content