Design a mobile that illustrates the difference between ounces, grams and pounds by having measuring cups of different sizes dangling from each rod, along with a card that notes the various different ways of representing those measurements. An example would be to have a rod with a 1/2 cup measuring cup attached to a card that notes the measurement can also be represented as 118 ml (mililiters) and 15 g (grams).
Create a mobile that outlines how to make a simple recipe, using metric measurements in each of the steps. If the recipe is for cookies, the rods can have decorative cards dangling from them that explain how much of each ingredient needs to be mixed with another, listing the ingredients in metric units. Hang chocolate chips from the mobile to add some decorative flair as well.
Make a mobile that explains how to perform a basic science project, listing metric measurements for each chemical or element necessary. A mobile about how to make your own silly putty would have cards explaining that you need to add 30 ml of glue to 15 ml of liquid starch, as well as 1 ml of food coloring, and stir it together. Decorate various parts of the mobile with the finished silly putty.
Construct a mobile that reflects the various different measurement systems throughout history. From one rod provide information on how the metric system was developed in 1668 and officially adopted by France in 1799. Another card can explain how the metric system is the dominant measurement system across the world, with the major exception being the United States.