I'd say probably meters unless it's a really big playground.
Meters, unles you are wieghing it.
The best unit is a metre.
METER
Meters
meter
The Unit Used To Measure A Train Can Be Kilometer.
Kilograms
Cubic kilometres.
The SI unit would be degrees Kelvin.
6 m would be used to measure flagpole. 600 m is a bigger unit.
grams
centimeters
millimeters
A kilometre. A megametre may be more appropriate but it is not a unit that is used much.
mililiters
Centimetres.