A mother hen might could hatch them, but couldn't raise them. I've raised several wild birds. People in the neighborhood bring them to me. I've always had success feeding them, when they are very young, canned cat food that is watered down from a syringe. They graduate to less watered down, over time, from tweezers. You have to be careful and place the food at the back of the throat. Don't give them water, just have it in the food. Its very easy to drown them. You also have to feed them constantly, depending on the bird. It seems as if mocking birds are never full. They need to stay warm and I have found a hot water bottle covered with a towel works best. A have also made a little cage out of two plastic boxes, that makes a great little nest. I wire tied them top to bottom. It fits in a big canvas shopping bag so that I can take them wherever I go for feedings, if I'm going to be out long. Yes, I've taken birds to wal mart, doctor's appt's, grocery shopping and almost anywhere else you can think of.
Its tough to raise them, but rewarding. When they hatch you can email me for more info on raising and releasing.
