Of course these units of measurement are also linked to measurements of area, and volume. Such forms of measurement each have their own unique names and ratios to deal with as well, but young children seldom have to deal with them. The measurement of weight also uses two systems. Officially ours is the metric one, with grams and kilograms. The reality is that when grocery shopping one finds both in use.
Many people feel the gram is too small and the kilogram is too large.
Meat especially is often labelled as so much per pound, and so much per kilogram. Besides that, a lot of food items come from places where ounces and pounds are used. Ask Canadian children or adults what they weigh and their answer will likely be in pounds. I know mine would be. Bathroom scales don't wear out that quickly.