Are they terrestrial or aquatic frogs? I have a terrestrial frog which the missus saved from the cats in one of my tanks and he is quite happy munching out on pinhead sized crickets.
Before I get jumped on for keeping a wild, native, diminishing species in my tank, it is only a temporary home until we get the pond built. There's not much point in putting him back into the (as yet) non frog safe yard with my cats prowling out there, he'd be lunch in 2 seconds flat (and almost was).