Add dry grass and dry leaves. Attach the new nest to a high branch or shrub as close to the original nest as possible. Make sure there are branches above the nest to shelter the babies from sunlight. Secure it with wire, strong string, hosiery or netting. You can listen for the noise of their being fed.
Baby birds create quite a ruckus when eating.
The mother bird can do the best job of raising the baby. If the mother bird and the nest are nowhere in site, you should retrieve the bird and call a Wildlife Rehabilitator. Your state division of wildlife management, the Department of the Interior - U.S. Fish and Wildlife Service, your local veterinarian, area animal shelters, state or local police or animal control officer should be able to supply you with information on how to contact them. A fledgling will be seen hopping around the ground, seemingly all alone. Usually, if you are patient, the parents will show themselves.