Height is probably one of the first ways we explore measurement with young children. Words like “shorter” and “taller” already exist in a young child’s vocabulary. How “tall” someone is visual and easily seen. Children are very interested in themselves, so conversations about how “big” or “tall” they are is engaging to them.
When I was growing up my parents measured my sisters and I against the door jamb of the kitchen. You could see our upward progress with names and dates. I remember thinking that leaving that evidence of our growth was so sad when we moved out of my childhood home. My husband and I have done exactly the same thing with our kids. When I look at it now, I can’t believe that they were ever so small.
You can measure your kids on the wall (covered with a piece of paper) and make marks to show each child’s height. You might place each child’s picture next to her/his mark so they can see themselves. This now means that the children can compare the heights of the children in their group.
Here is a link to a lesson plan that involves length measurement using a nonstandard unit of measure.