How did you teach them what "hot" meant?
I told my son, who was out with me after I changed the belt on the riding mower which then started to smoke due to routing it over a guide instead of under, not to touch it it was "hot"! As I was walking toward the garage to get my tools (the mower was off) he reached under to touch the belt and got a small burn on his finger. After that, he knew what "hot" meant. Before that I'm not sure.
A space heater.
FYI, not my space heater and I wasn’t there at the time.