Feed it Dove and Quail seed mix from your pet store if it is big enough to eat that, or give it parakeet mix that has been treated with vitamins and minerals so that it has enough of what birds need.

Let the baby bird eat all it wants. Keep that cup full, maybe get a larger cup. Keep food (and water) available at all times.

I have a baby pigeon that's about 3 weeks old and he constantly wants to eat. I feed him grains (wheat) and he seems to like it but 1-4 hours after feeding him as much he will consume, he gets up and starts making a squeak noise and starts pecking me and eating things off the floor until I feed him again. I usually feed him 4 times a day, as much as he will consume each time per feeding. Is that too much? Why is he always hungry?