HI Botanist, glad I 'found' you as I'm trying to do the same - raising Rana temporaria / common frog. So far my tadpoles are doing fine. I've mainly fed them algae I found in a pond but also lightly boiled dandelion leaf, bread and a bit of boiled egg. The boiled egg thing I read somewhere as advice - they're eating it although they're still supposed to be vegetarians?! They also nibble on the watercress I put in the bowl (mainly on the roots I think). Can't believe how quickly they dirty the water though, wish I knew what eats their poo in the wild - water snails, shrimp, stonefly larvae, other insect/larvae??
As for carnivorous stage - I think aphids might be easy to find and small enough for em to digest? perhaps tiny water snails?

I have some pictures posted on facebook.com/fealebiodiversity of them and will keep posting their development there (album amphibians) - if I manage to keep em alive that is! Do have a look and keep me informed how yours are getting on!