Nintendo Switch

So my Mom is getting my boys (ages 8 & 9) a Nintendo Switch for Christmas this year, and I've been tasked with getting them a game to go with it. What is the absolute must-have game (or two) for that system? I'm a PC/Playstation guy that hasn't played Nintendo since Game Boy. I know I know..

Get Super Mario 3D All-Stars because it goes away at the end of March and you only get one shot at it.  Failing that, Super Mario Odyssey is probably one of my favorite games, ever.  Also people will tell you Zelda Breath of the Wild, but I'm not a Zelda guy so I can neither confirm nor deny.  I'm a Mario Guy myself.  

That being said, you can always play it safe and get Mario Kart 8 because you're kind of legally obligated to buy a copy when you get a Switch.  It's just the law, I'm sorry, I don't make the rules.