Oh man, former tadpole catching professional here! I spent every summer catching and caring for my tadpoles. I actually caused the salamander population to go extinct in my pond because I caught so many babies...
It was so much fun!
First thing, are they really frog babies or are they salamanders?
Salamander tadpoles will have sticky-out-y frilly gills while frog gills aren't obvious, that's the way to tell them apart at the first stage.
If they're salamander babies (what I had) going to the pet store and buying freeze dried daphnia, until they grow back legs, and freeze dried bloodworms when they start growing legs works well. You basically want to feed them kind of like fish, put in enough that they eat it pretty quickly. I liked to give a little extra to make sure they're eating enough as well.
They also adored live mosquito larva.
Frog tadpoles need vegetable matter. I used to blanch the living daylights out of lettuce and they loved that. They don't need/want meat like salamander do. Basically any vegetable, cooked until it's really soft, will do the trick. I've heard that lettuce and cucumber slices are real winners.
Salamander tadpoles might eat the fish food but I doubt that frog tadpoles will.
I don't know how much you know but I'll just share with you the other things I learned while I was being "Tadpole Captain"
An important thing is that unless the tadpoles have something breaking up their line of vision, the biggest one WILL eat the smaller ones until he/she is the last baby left. Lemme tell you, it's SUPER traumatic checking on "your" babies and find that they're eating each other!
I liked to get those super cheap plastic plants from the pet store, tie some rocks to them with fishing line, and stick them in the tanks. I found that about 2 plants that went from the bottom to the surface of the water per 5 gallons was about right. ETA:
I'm not super experienced with frogs, since I primarily had salamanders, but this website looks to be pretty helpful and complete: http://allaboutfrogs.org/info/tadpoles/index.html
Also, make sure to always dechlorinate the water before adding water to your buckets/bins. I had so many babies die because I didn't do that! That was also traumatic, so sad.
When I was really doing it, I found that using 20+ gallon Rubbermaid storage bins worked super super well. They were cheap and the tadpoles seemed much more at ease in them then they did in the 5 gallon buckets I started out using. Before I started using the larger tubs, I had about a 75% mortality rate but after I started using the tubs my mortality rate went down to about 25%.
Tadpoles are so much fun! Thinking about this makes me want to go search some out and start playing with them again.