Why won't the baby chicks come out?

My family has had two baby parakeets that are about six weeks old now. However, there seems to be a problem with the two...they refuse to leave the nest box. I've been keeping my distance to let the parents do their thing with the chicks, but the only thing that happens is they go in and regurgitate food to the chicks instead of weaning them. Neither do they seem interested in kicking the babies out. They just sit there while the babies huddle in the back, and I'm starting to wonder if I might need to something about this. Any suggestions?