After introducing safety symbols, give the kids the following scenario:
“You are doing a dangerous experiment in the Science lab, you have to leave your dangerous liquid and come back. Leave a note describing what it is so no one will touch it…”
I leave out a flask (it's so sciencey and mysterious to them!) filled with water and food-colouring. They complete the attached sheet, coming up with a name, its danger symbols and what it would look like if someone touched it.