Hello and welcome to FF! Can you check local pet shops for wingless fruit flies? From there can go into pinhead crickets, etc. Food should be no bigger than distance between frogs eyes. Will also need CA/D3 and vitamin supplements (recommend Repashy or Rep-Cal brands) and can use these dusting schedules:
http://www.frogforum.net/food-feeder...schedules.html.
Since it's a baby, recommend keeping it on a coupe layers of damp paper towels. Only use dechlorinated tap water (Seachem Prime is good). A water dish (bottle cap) with water no deeper than frog's chin can be added to enclosure, with some artificial silk plants for frog to feel secure. If frog eats the flies, it's doing good.
Recommend go with this care sheet information until we figure out the frog species:
Frog Forum - Gray Tree Frog Care and Breeding. Good luck

!