a quick and simple food for baby fish is boiled egg yolk. Boil an egg for 10 minutes and then remove the shell and the white bit. Put the yellow yolk into a handkerchief and squeeze it through the handkerchief into a small container of water. Put a lid on the container and shake it up.
When the babies start swimming about, you shake the egg yolk mix up and use an eye dropper to suck it out and squirt it around the tank near the fry.
You can also buy liquid fry foods that are a similar thing and you add a few drops to a small amount of water, shake well and add to the tank.