Family coverage, and any additional amounts for dependants, must be checked against the official FAQ at the time of application. Under the employment-based categories, a spouse and unmarried children under 21 are ordinarily derivatives.
Check the family terms on the official page, then the category
Hypothetical example: a Quispamsis executive assumes one payment covers his wife and two children aged 15 and 19. The official framework should be read directly for whether dependants are included, whether additional amounts apply and how they are treated in vetting; those terms are set by the official program and can change. Separately, the underlying employment-based category ordinarily allows a spouse and unmarried children under 21 to immigrate as derivatives.
The 19-year-old's age at the relevant stages matters, because a child who turns 21 before the process completes may lose derivative eligibility, subject to statutory age-protection rules that require their own analysis. The family should record each person's date of birth and current status, decide whether the older child's own plans might warrant a separate route, and avoid assuming that the gift alone determines who immigrates.