Family inclusion follows the official program terms and the rules of the underlying immigrant category, which ordinarily allow a spouse and unmarried children under 21 as derivatives. Confirm the current terms on the official page, since the program's family provisions and any per-person charges may change.
Derivative rules come from the immigrant category, not the card
The Gold Card framework produces permanent residence through an existing employment-based classification, and derivative status in those classifications extends to the principal's spouse and unmarried children under 21. Whether the program charges an additional amount per family member, and how it treats children who are close to 21, are questions the official FAQ addresses and which should be read at the time of application rather than assumed from summaries. The Child Status Protection Act may apply to derivative children as in other employment-based cases, but its calculation depends on petition pendency and visa availability, so a Lac-Beauport family with a 19- or 20-year-old should get that analysis before paying a fee that will not be refunded.
A child who marries loses derivative eligibility. Nothing in the framework authorizes a spouse to work or a child to study in the United States while the application is pending, and a family member who wants to be in the United States sooner needs their own nonimmigrant status.