"could have happened to anyone"

Uh, sure, maybe anyone who wasn't 16 years old. I completely blame the company for allowing a 16 year old to operate dangerous equipment, let alone without direct supervision.

If his two coworkers were only alerted to his injury after the kid phoned his boss, got disconnected, texted him a picture, then the boss phones the coworkers, they were absolutely not close enough to be supervising that kid even with "hearing protection". That would be like 2-3 minutes at least for that process but likely took longer.

You're telling me there were no better jobs the kid could have been doing while the coworkers operated the mulching machine?