That Cosmere RPG looks interesting ! I found Brandon Sanderson's worldbuilding to be fascinating, although the books became a bit of a slog after a while.

If your son is into spy stuff, when he's a bit older you should introduce him to Killer, originally published by Steve Jackson Games waaaay back in 1981. I don't know if you know it but it's basically a live-action assassination game, where water pistols and Plasticine (and anything else non-lethal crooked minds can think up) take the place of real guns and explosives. You need enough players to make a circle, where each player draws a name at random who is their target, but doesn't know who is their assassin. It's huge fun but definitely needs agreed rules to prevent it getting out of hand (e.g. no assassinating people while they are at work). My best "kill" was getting my target by total surprise at long range with a super-soaker as he got home at about 1am, having lurked hidden in his road for a few hours 😁