Raising a baby sparrow?

I found a baby sparrow at my stable while I was riding my horse. His eyes were closed and he only had some pinfeathers. I took him home (I know they say to leave them because the mom will come and care from him, but we have a barn cat...) and warmed him up. I am feeding him kitten food because it's high in protein and nutrition. Now he is a few weeks old and is fully feathered even though they are just baby feathers. My original plan was to release him into the wild but I noticed he is really attached to me. He is learning to fly now and when he does, he flies to me and perches on my shoulder and I have handled him to aid him in his flying lessons. I am afraid that if I release him, he won't know how to fend for himself. Any suggestions?