The best thing to do is to go back to the pet shop where you bought them and ask what they are used to being fed with. What they will eat depends on what they are used to eating.
Also are they really small? If they are you might have a problem feeding them, I bought a couple a while back that were really small, and they would only eat things that moved, they would sit and wait for it to wriggle, which meant that they would eat nothing but live food. Well in the end they died because the fish liked live blood worms too. After moving house I went to my LFS and saw his frogs eating just the fish food so Iasked him why mine never did as well and he told me that because they had been reared on live food they wouldn't eat anything else, and that often very small frogs do not survive. So asking the pet shop is the best thing to do.
Ideally they should be fed frozen bloodworms.