Squid Game is definitely not for kids I’ve only seen ep1, but yeah just on sheer body count and amount of blood I would not encourage parents to let their kids watch it. Certainly not primary-aged kids, anyway. Secondary age may be a different matter. Like Dan, I was allowed to watch some pretty bad horror from a fairly young age and I actually thank my mum for that. She played it perfectly. There were still rules but my sister and friends lived near a video shop that didn’t care about the age ratings so we were allowed to discover our own limits and didn’t become Disney kids. Thank you, Mum.
As for the violent playground games, that’s nothing new. As long as no one is killed then it’s just a regular playground game, albeit with a new theme. If it does get particularly bad, schools will ban them just as they banned British Bulldog when I was a kid.