That video is shocking. It should be a no-brainer that kids are not allowed in a home exercise room or on the equipment. Maybe all machines need a child-safety lock, where just pressing "start" won't activate the machine unless there's another code punched in by the user.
Years ago I was the family spoilsport when I told my two nieces (ages 9 and 10, one barefoot and one in flipflops) that they could not use my treadmill. Got grief from DH as well as my brother-in-law, both of whom thought I was being too controlling. There's a reason kids shouldn't play around workout equipment, people!