We're getting into panfishing season, so bait shops might be a source of very small minnows, leeches, mousies, etc. that are commonly used for sunfish, perch, crappies, etc.
Stores that sell reptile supplies will have mealworms, crickets, etc.
The little ones are very surface-oriented, so it might help to pick up a "worm blower" at a fishing tackle store. It's just a little squeeze bulb with a hypodermic needle on it; lets you inject a tiny air bubble into a piece of earthworm or other food that would sink otherwise.
Floating plants or other surface cover will help calm them and get their minds back on eating. They'll be easy to switch over to frozen or prepared foods once you get them started on live.