The group of boys might have been young adults. The Hebrew word used here can mean a young adult who is still learning a job. For example, Solomon asked God for wisdom because he was young and inexperienced (1 Kings 3:7). Joshua's spies in Jericho were also called by this term (Joshua 6:22–23).
Calling someone baldhead was disrespectful. The young men told Elisha to go away (literally go up), mocking his role as Elijah's successor, given by God.