Baby sparrow

Last wednesday I found a baby sparrow. He (or she) had feathers but they weren't fully grown in yet. So I waited to see if mama was around and going to feed him, but no mama. so I put him in a box with some towels and the only thing I had here at work was nutra-grain bars. so i wet some of those and mashed them up and he seems to be doing okay. My only problem is I dont know when it is time to teach him to fly or when he will eat on his own. He has pretty good balance already and he kinda hops around and flutters his wings a little. so what do I do when it is time to let him go? will he do okay? oh one more thing. why dog food?

any suggestions would be great.
Thanks so much.

Amos