Right now you can probably find a Switch bundled with Mario Kart, so you save money and get a good game for the kids right away. There are enough games to keep them busy for years.

On the other hand, if they want the newest games, it sounds like the next one should come out next year sometime.

Either way, a couple games I'd add as recommendations for kids:

Kirby and the Forgotten Land
Mario Party games
Overcooked