From the picture you posted, it appears that your froglet has not completely resorbed its tail yet. Until they completely resorb their tails, that is where they'll get all of their nutrition. No need to feed until this has happened. Once the tail has fully resorbed, you can feed them flightless fruit flies. They are very tiny and easy to breed. You can pick up a culture at Petco for about ten dollars. They do tend to climb the walls, and can escape. If you use a VERY thin (allowing for ventilation) cotton cloth secured to the top of the terrarium, it will prevent escapees. (I tied a ballon, the kind for balloon animals, to form a large rubber band of sorts for this purpose.

As for the water dish, they really don't need it at this stage. Until they are about three to four times their initial morph size, they will do fine in a bare terrarium with paper towels as substrate. You don't want standing water, but do keep the paper towels wet at all times. Just after morphing, frogs are horrible swimmers. :-/

When feeding the fruit flies, you'll want to do it just before wetting the paper towels, not after. Damp towels won't hurt them, but they'll have problems if the towels are too wet.

I'm no expert, and actually have very little experience myself, but I have *some* experience (and spend way too much time reading care sheets). Hope this helps.