> Do what kids in the 80's did, and many still do: go to the local playground, and ask if you could also play with them.

I was a stay at home dad for a couple years, and I made a lot of long term friends this way. In one case I saw a guy riding his bike with a 2yo on the back so we chased them down and asked if they wanted to hang out and do bike nerd stuff together. That was almost 6 years ago and we're still friends