This website is a good resource for sparrows:
The care and rehabilitation of injured and orphaned starlings and sparrows. Information resource about European Starlings including baby bird care, starling diet, sexing, bone fracture repair and history.
Here's more specific info on baby care:
Care of baby starlings including info on how to keep a nestling warm, what type of formula to feed it, how to handfeed it and how often to do so.
There's a hand feeding recipe here. I used this for my sparrow but didn't add the egg or vitamins.
I don't remember now how old Spee was when he weaned. The first thing I gave him when I noticed
him picking at things was millet spray. When it seemed could eat that on his own I weaned him onto
finch seed, Mazuri Insectivore, and cooked mixed veggies (corn, peas and carrots). Every now and then
he would also get very small pieces of egg white and/or very small pieces of cashews.
He also had a small piece of cuttlebone available.