I've not tried any frozen foods with mine, so I can't say whether they would take them. Live blackworms are a handful, even for adults. A single average-sized blackworm is longer than an adult sunfish. Even frozen bloodworms would be on the large side for prey. I imagine they do some foraging and might eventually try out something like frozen bbs, but like notophthalmus said, live is better (won't foul as fast, more whole organisms, more nutritious). For raising fry you will need live foods of microscopic proportions. They are lazy predators as it is, and they need some movement to attract their attention. In the case of fry I use mostly infusoria and vinegar eels to start, and eventually move up to baby brine (freshly hatched) and microworms.