Originally Posted by
U-Ute
TL;DR: Look at the games available for the platforms and pick the platform that has the games you want.
The fee is only if you want to play games against others online. I have a PS4 and don't pay any monthly fee.
The key is what games you want to play. If he really wants to play Nintendo games, then you have to go with the Switch. You can't get Nintendo games on any other platform. Then you have to live with the fact that games like FIFA and Madden either don't exist or are poor ports, but you'll have Mario and Link. Given his age, you probably don't care about M rated titles (Call Of Duty, Far Cry, TitanFall, Destiny) and they may gravitate to the sports titles (FIFA, NBA 2K, Madden). The good news is that those titles are pretty much available on both XBox and Playstation, so it doesn't really matter which one you buy.
The biggest differentiation between Microsoft and Sony is probably in online (XBox Live is great on my 360) and support for indie titles (which Sony has adopted with the PS4). Nintendo was way behind in online support, and I've been out of the industry for over a year now, but I'd be surprised if anything has changed much in that regard for the Switch.
So I'd start with looking at the games you want to play, see if any of them are specific to a console, and if so, that's the console you get. If it doesn't matter, then you'll have to look and see if there are any second or third level features that pique your interest - PS4 has a VR headset for example and XBox has HoloLens. I think there is now 4K support available for those systems if you have a TV. Those are definitely niche as there isn't a whole lot of support on the game side for those features yet.
My personal opinion is I prefer the PS4 over the XBox One. My boys are 8-12 years old and we focus mainly on sports titles. The horsepower of the PS4 and the XBox One are pretty much equivalent, so you don't get much of a performance difference between the two machines. The reason I prefer the PS4 has more to do with how easy it was the develop on more than anything consumer related. I know people who own an XBox One who love them.