LPT: when taking young children to the playground instead of saying they have 5 minutes left tell them they can go on 5 more "rides". This gives them something visual to work with and helps stop tantrums. Also helps with numbers when counting down to the last ride.

I must warn that if you have a smart kid they will try and do zero as they see it as a number. Things like swings give a set of 10 pushes for one go etc and sandpits maybe see how long they stay on (this might be harder to get then out of). Worked with my son from when he could count so about 3 ish. He used to tantrum a lot when leaving but doing this prepared him for us leaving and stopped the tears. Plus he got to use numbers which he enjoys. He is now 5 1/2 and we still count down using play equipment.