Taking my 5 year old son to the playground can be a great workout. We got there this morning when it was empty, so he wanted to play chase. If I do that while jumping over benches, climbing fences, climbing through kid-sized tunnels, and making sure I did a lot more work than him, I get in a lot of functional movement. Later on he and some other kids drafted me into another chase game they dubbed “cops and robbers.” (I was the cop.) The game was for me to chase them around, appearing to be “menacing” without actually catching anyone.
Sometimes you get some weird looks from other adults. It’s socially acceptable, as a 48 year old man, to play with children by humoring them a bit. It’s odder to actively climb around on the equipment and participate in games. But it’s a lot more fun.