- Millicent (Milli) Mathison: The six-year-old leader of Steampunk Umizoomi. She has the same powers as the main universe Milli, but for measuring, she has a headband that ejects tape measure.
- George (Geo) Mathison: Milli's five-year-old brother and the Mechanic/Inventor of Steampunk Umizoomi. He carries with him a lightweight machine that shoots out shapes of all sorts, similar to the main universe Geo's shape belt.
- Bot: He is, as Geo descibes him, "a caculator with arms, legs, and a personality." While his main purpose is to caculate numbers, he shares some of main universe Bot's powers such as his belly screen.
- UmiCar: Resembles a Stanley steam car more than a futuristic car.
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