I mean - whatever you can imagine? We’ve played chess, worked on learning languages, picked up musical instruments, learned to ski, learned to hunt mushrooms, electronics projects, woodworking projects... sure sometimes you have to keep it at an age-appropriate level, but there are things I want to learn and if I include them then they benefit and grow as well. My kids are now at an age too where they are starting to pick things up on their own and then they can teach me.

Learning swimming at 38 because I want to swim with my kids who can swim well already

Cookery? Languages? Music? Singing? Dancing/Excercise?

To be honest I did those kinda things already, except for the singing, but having a small child those are the kinda things he likes at the moment. No doubt his tastes will change over time, but I'm gonna try to join in with his interests at least until such time as he doesnt' want his "uncool" dad doing so.

Geocaching is an easy hobby to learn (and much cheaper than it used to be for anyone with a smartphone) and gets you outside with the kids, who consider it a treasure hunt. It might be a little challenging during quarantine, but it’s a great way to get some exercise and explore the area around you.