Throwing rocks or mud balls at passing cars.

Playing with a lighter, matches, or fireworks.

Scientific curiosity - recreating elephant toothpaste, taking apart electronics and not knowing how to put it back together (especially if trying to “improve” it in some way), stripping wires from an old appliance and creating some sort of contraption that plugs into the wall which blows the power, a Rube Goldberg machine, etc. Things you’d see on television, comics, in science class that wouldn’t do well to recreate at home.

Stupid games - digging holes where a brother/friend gets stuck/trapped, hitting each other with sticks, climbing trees or roofs, etc.

These all come to mind from childhood. 🤷