Surely you’re overthinking it and over specifying the pedals if he’s just using the bike to get around on? Just tell him to drop his heels a bit to stop his feet bouncing off. Either that or just stick the crappy OEM ones that came off the bike back on and absolve yourself of the problem.
Plastic pedals help because they weigh less so hit the shin with a bit less force assuming the rider comes off both pedals and the cranks are just spinning.
The mistake you made was assuming that the rest of the world cares about anodised bling pedals with big pins on their bike. To a 13 yr old a bike is just what get’s them to a mates house to play call of duty or the Spar for 3l of White Lightning. If he’s really lucky he’ll pull a massive skid infont of some girls and pull one of them before graduating to a Corsa and doing handbrake turns in a few years.
unless he want’s to look a wee bit stupid in front of his pals.
How about introducing him to MTB clippers pedals and shoes with recessed cleats?
No one looks good in SPD shoes, even before they try to walk/run/play football/pull girls in them.