M.D.
I took a kickboxing class (not aerobic kickboxing, but true kickboxing) as an adult and LOVED IT. Boxing is not quite the same, but similar and I would whole-heartedly support it. You can talk to the instructor, but my guess is that he would be working out with a bag learning form for quite a while, not in a ring sparring other kids. That is something to ask at the gym.
ETA: I just want to add that talking to the instructor would be essential for me. If the place puts kids quickly into a ring to box each other, I would not be in favor. But you say it's a class, and I would expect that classes would be focused on proper form and strength training using bags, and that is what I would have no problem with.