Why do we use rulers? Where did the inch come from? Why is a foot 12 inches? Isn’t that random?
Standard units of measure have their place in the larger world. They are defined, agreed upon, adopted, and used so that human beings can know precisely the “measure” of a physical quantity. Wouldn’t it be strange if a gallon of gas was different at every gas station? It would be complete chaos.
Young children can be introduced to standard units of measurement, although they may not be as interesting as using a more engaging tool, such as links for length, or pebbles for weight. A ruler is a good way to begin. The children may be really interested to know, that according to lore, the origin of the foot came from measuring the foot of a man; many say the king. They can compare their own feet to the length of the ruler to determine if their feet are bigger or smaller than the king’s.
They can look at the ruler and see the divisions and even count the numbers. You can provide several objects for them to measure with the ruler. It is important to explain that because you are using a “standard” unit of measure, their answers to the questions should be the same. That is the purpose of using the same standard.
I might even get every child her own ruler. They are inexpensive and you may find them measuring things when you least expect it.