New to gaming consoles - what do I buy my kid?

I don’t know anything about video games or consoles since we’ve never had one. We went to GameStop to get a gift, and my 6-year-old played with a Nintendo Switch there. Now he really wants one, especially to play Mario Kart, and we’re thinking about getting it as a family gift for Christmas. I’m looking at the Nintendo Switch OLED bundle, but I’m not sure what else I need.

We’re a family of four, and I want to know if we need the Nintendo Switch Online membership to play games together at home. Some bundles come with a 12-month individual membership, but I’ve seen there’s also a family membership option. Do we need either of these to play together at home? If I get the online membership, does it give access to all the games, or do I still need to buy each game separately?

I don’t want my kid to play online or chat with others since he’s only six and this is our first console experience. Plus, we don’t know anyone who plays, so I’m not sure if we need the online membership at all—unless it gives access to all the games. If it does, then it might be worth getting so we don’t end up with games all over the house.

Also, what about controllers? I see they’re called Joy-Cons. Does one set of Joy-Cons work for two people, or just one? How many sets of Joy-Cons do we need for four people to play together? Are there any good family games we can enjoy?

Please break it down as simply as possible. I need to explain this to my wife too. Thanks!