I'm guessing he probably signed a waiver that explained that broken limbs were an assumed risk of jumping on trampolines, and his legal recourse is fairly limited.

Something like:

http://www.skyzone.com/Portals/0/waivers/vannuys.pdf

I acknowledge and agree that I and the Child are participating voluntarily at our own risk, that the actions or activities of other customers, or the actions or inactions of Sky Zone Facility employees, could cause me or the Child significant bodily injury (as described herein), and that SZ is not responsible for the actions or activities of customers using the Sky Zone Facility or the negligence of its employees in supervising the Sky Zone Facility or its usage, including actions, activities, or omissions that result in such harm. Some of the risks include the following: (Note: This list of risks is illustrative only.) a) Participants may suffer cuts, scrapes, bumps, bruises, the transmission of disease strains, and allergic reactions through use of the Sky Zone Facility equipment or contact with other participants or surfaces they have contacted. Participants may sprain, pull, break or otherwise seriously externally or internally injure their head, face (including nose and teeth/jaw), neck, torso, spine, arms, wrists, hands, legs, ankles, feet or other body parts as a result of falling off the trampoline(s) or other equipment, landing improperly on the trampolines or other equipment, or making contact with other participants. Such injuries can lead to paralysis, disfigurement or death. Participation may result in heat stroke, heart attacks, dehydration and other exertion-related medical events. b) Participants often fall on each other resulting in broken bones and other serious injuries. Double bouncing, more than one person per trampoline, flipping, running and bouncing off of the walls and wall-mounted trampolines, and other participant body movements (whether planned or unplanned) can create a rebound effect and lead to unpredictable body movements and anticipated or unanticipated bodily contact, any or all of which can lead to serious injury. c) Traveling to and from trampolines can result in similar physical injury (even if the participant is not him or herself bouncing at the time)