I had a case kind of like that, but a little different: I found baby bats, called our local SPCA, and got directed to an expert who lived about a half-hour away and knew what to do with them. I left them with her.
Although in my opinion it would be safer to bring them to an expert, if they're fledglings, they might be OK with what you can provide.
I would probably keep a heat lamp on/heating pad available to them and try to tempt them with food a lot. Multiple times per hour. Maybe bugs, worms, fruit, bread? Everything common sense dictates (use paper towels, etc.) I have read not to feed them milk, honey or eggs. My only worry is how you will reintroduce them to the outdoors once they can fly (having been fed by hand, can they find food on their own?)
Alternatively, you could put them back where you found them and keep an eye on them for a few hours to see if the parents return to care for them. Most fledglings ARE fed and cared for by their parents on the ground before they can fly--when they learn to fly the parent takes it from there. You might keep an eye out for the parents, because they will probably come looking for the babies.
Good luck!!
It's a wonderful thing of you to take them in and care for them.