Not sure how you feel about Epic Games, but if you create an account for him you can start claiming the free games that he will eventually be able to play when he I older and has a PC. In the mean time he would have access to a couple free games like Dauntless which highly recommend, is totally free and very similar to Monster Hunter World. He would also have access to Fortnite which I know for most people is love or hate. The pic below has all the Epic Games that are always free, I believe most are playable on the Switch.
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On the Nintendo Store there is a free game called Super Kirby Clash which is free. My kids just started playing this and they seem to really like it.
Lastly, this...
Are you looking to play a new game without spending any money? Here's our list of the best free Nintendo Switch games to help!
www.androidauthority.com
Hope this helps Bro!
I am huge supporter of kids playing video games as long as there is some balance with RL/Outside, something I probably need to do a better job of because I most likely spoiling mine.