Can you be held liable if your 11-year-old son is accused of breaking the arm of a 5-year-old while playing on a trampoline in the younger child's yard?
Liability is almost certainly going to lay with the owner of the trampoline.
Trampolines are considered an "Attractive Hazard". meaning they attract people , especially children to use them. Much the same as a carnival ride or an acccessible neighborhood swimming pool.
The above being common knowledge it is amost always accepted that the owner (barring rior legal waiver) of the attraction is responsible for proper supervision and safety as well as resulting liabilities, not the user and certainly not a third party who has no control over access to the trampoline.
Not criminally liable, but you could be subjected to a civil suit and found liable for the injury.