**Core Concept**
The question involves identifying a reducing sugar in a child's urine, with negative results from glucose oxidase and Seliwanoff's tests. This scenario points towards **carbohydrate metabolism disorders**, specifically those involving sugars other than glucose.

**Why the Correct Answer is Right**
Given the negative glucose oxidase test, which is specific for glucose, and the negative Seliwanoff's test, which is used to detect fructose, the reducing sugar is likely to be one that is not glucose or fructose. Since the child is one year old and has a reducing sugar in the urine, **galactose** is a plausible option, as it can be present in the urine in conditions like galactosemia, where the body is unable to properly metabolize galactose.

**Why Each Wrong Option is Incorrect**
**Option A:** This would be incorrect if it were glucose, as the glucose oxidase test would be positive.
**Option B:** If it were fructose, Seliwanoff's test would be positive.
**Option D:** This option is not provided, but typically, other sugars like lactose or sucrose are not directly tested by these methods and would not be the primary concern in a scenario like this.

**Clinical Pearl / High-Yield Fact**
In cases of suspected carbohydrate metabolism disorders, like galactosemia, it's crucial to identify the specific sugar through appropriate tests to initiate the correct treatment, as undiagnosed conditions can lead to severe complications, including developmental delays and organ damage.

**Correct Answer:** D. Galactose.