What are some good switch games for kids to keep their brains active?

My (then) four year old had a lot of fun with Donut County. For the most part she figured it out entirely on her own and even managed to beat it. And given the nature of the puzzles involved, I like to think she learned a thing or two at the same time.

My 5 year old god daughter loves both Breath of the Wild and Untitled Goose Game. While she's not particularity good at either, both are free-form enough for her to experiment and try different things as she learns how to navigate and problem solve in a virtual space.

If you want something with a bit more challenge or a tighter focus on puzzles, there's lots of great options. Some of my favorites include World of Goo, Portal & Portal 2, Tunic, Ori and the Blind Forest, and Baba Is You. That last one gets fairly difficult, even for adults, but it's one of the most unique puzzle game concepts I've ever seen.

Also, as /u/TuckTales mentions, the Lego games are great for kids of all ages, however, I would recommend avoiding them due to Warner Interactive's systemic abuse of both their employees and customers in recent years.