We used to take our tiny 3.3 HP stainless steel boat from Ephraim WI to Horse Shoe Island and the Strawberry Islands. The engine had a tiny built-in gas tank, so we had to carry a large tank to refill it during the trips. The boat was very tippy and could have been swamped very easily. Also, it leaked except when moving. I doubt that our parents knew what we were doing because it was very dangerous.
We also used to make silver coins (remember them?) shiny by rubbing mercury on them. We had a pint bottle half filled with mercury. I used to do experiments with electricity using mercury and you could see the mercury vapor rising. At that time, no one knew any better. And now people are worried about the tiny amount of mercury in compact fluorescent lights.
Once we found a stone shapped almost exactly like a quarter pound of butter. We colored it yellow with a crayon, put a butter wrapper around it, and put it into a pound butter box with 3 sticks of butter in it. Our mother didn't even notice the difference in weight. She thought that the color looked a bit off, but didn't realize what it was 'til she tried cutting it. At least she thought that it was funny.
I unbolted and removed the fan from my mother's 1950 Chevrolet. It didn't overheat except when the engine was running with the car standing still. After a few weeks, mother was sitting in the car talking to a friend outside of the car. Eventually, her friend said, "Mary, your car is steaming!!" So, mother did the worst thing possible. Instead of driving off quickly so that the moving air would cool off the engine, she shut off the engine and water and steam shot out. She and dad were not very happy with me.