I am no expert so please do research and don't take what I am saying as law.

From what I have seen you keep feeding the tadpoles until they leave the water. They will not eat once they leave the water until their tail has been fully observed. Once it had they need to be offered food daily. Make sure the food is small enough for them to safely swallow. Springtails are a common food for newly morphed froglets. Small fruit flies are also good as are pin head crickets.