Be careful not to get fluid in the breathing tube in the floor of the mouth just behind the tongue. Clean food from the beak and feathers with a moist tissue. Later the bird will take thicker food and will eventually open the beak when it sees food or it may even squawk when it wants food. Stick the food to the end of a pointed popsicle stick or a drinking straw cut on a slant and give it to the bird. As the bird grows it will eat more, but less frequently.
Birds have a high metabolic rate and a high energy requirement.
Bread crumbs and milk are not sufficient. You have to put the food into the baby. Feed it when it asks for it. When it has enough it will collapse and sleep until it is hungry again. That is where his esophagus is and if food gets lodged in there he will choke.