I don't believe in exposing children to unnecessary treatment. Do I really need to treat circumscribed scleroderma?

No. Treatment is not essential however treatment will cause area to possible resolve quicker and decrease scarring and possible color change. Topical medications are only partially effective but do not have side effects. Oral medications effect is variable.
Optional. Circumscribed scleroderma can leave deep scars so I would not hesitate to treat if the lesions are on the face. On the other hand, the treatments are not always successful and the disease does not involve internal organs. All treatments have at least some risks.
Thick skin. Scleroderma is an autoimmune disorder, affecting mostly females, that causes thick, hidebound, areas of skin. It can be in small areas. Sometimes caused morphea, or systemic, which may include large areas and thickening of the internal organs like the esophagus or lungs. It is difficult to treat, and if there is only one small area, you can elect to not treat it, hoping it will go away by itself.