Legal Question in Personal Injury in Massachusetts

Re: Who is liable for this injury?

I would be quite shocked if the summer school had not required the parents to sign some sort of Release or Waiver of Liability as a condition to his being enrolled in the summer program.

In my opinion, the child has already been through physical trauma (from which he will probably quickly heal), and he should be spared the emotional trauma of a lawsuit (with possible testimony, deposition, fighting, etc.)

Even if you were able to file a lawsuit for the boy (as his Next Friend or Guardian), which I am not sure you can, it doesn't sound like the teachers or the school acted negligently. You would need to prove that simply having monkey bars was negligent, or that he was negligently supervised, or that they somehow reacted negligently to his injuries.

You indicate that they were not watching him the moment he fell off the monkey bars. Would watching have kept him from falling off the bars?

If not, perhaps you would argue that it was negligent to allow him to use the monkey bars. Any argument that it was negligent for the teachers to allow a 7 year-old on monkey bars would probably fail also - do we really want to keep 7 year-olds off monkey bars?

I would just leave it alone, and help the boy make this broken arm a distant childhood memory.