Measure the room with a $2 coin
During one of the STEM hours in our sessions, where they were learning about measurements, I asked the older kids to tell me how many $2 coins could they fill in a room of arbitrary size.
The little ones got a simpler version, where they had to figure out how many coins could they fit on an A4 printer sheet.
This involved some steps for the both of them, the little ones essentially used an actual coin and multiplication to roughly figure out how many could they fit in the width and height of the paper.
The older ones had to develop a bit more understanding of the volume. They also figured out the diameter of the coin from the internet or by using a vernier calliper. Everyone was able to solve it but the huge answers they got surprised them all.