They will get about 3-4cm long (body). I feed my mom's frog frozen brine and mysis shrimp. They are pretty much carnivores, so any meaty food is fine. Pelleted food for community fish may have too much plant matter in it. It won't hurt them, but I'd make sure they get some frozen brine shrimp or the like as well. They WILL eat anything that fits in their mouth and is not quick enough to get away, that includes endler and guppy fry, so keep that in mind.
When I can no more stir my soul to move, and life is but the ashes of a fire
When I can but remember that my heart once used to live and love, long and aspire
Oh, be thou then the first, the one thou art, be thou the calling, before all answering love
And in me wake hope, fear, boundless desire.