You should not need to feed them. Whilst they are morphing their insides are undergoing major changes. The digestive system has to alter from an herbivorous/detrital diet to a carnivorous one. Not until they are fully morphed froglets will they be able to eat again, at which stage they will be ready to be released where they came from. If the collection area is on your property, then you are entitled to keep a maximum of two of each species (up to a total of 8 frogs), so long as they are “of least concern” in conservation terms. Small frogs simply require smaller food, be that crickets, roaches, silkworms or whatever. Frogs have relatively large mouths for their size and as long as they can fit it in through their mouth, they will swallow it. So feeding small frogs is very much easier than feeding small lizards.