A spouse and unmarried children under twenty-one may be included as derivatives. Adult children, parents and other relatives are not derivatives and would each need an independent basis.
Count the birthdays before you count the money
Derivative eligibility is narrower than families expect, and the boundary is drawn at the spouse and unmarried children under twenty-one. A twenty-two-year-old in university, a parent who would move with the family, and a sibling are all outside the case. Because the process spans years, the age of a child at filing is not the only relevant date, and statutory provisions exist that can, in defined circumstances, protect a child's age during certain periods of processing. Those provisions are technical and their application depends on the facts and the priority date, so a family with a child aged sixteen or older should have the calculation done properly at the outset by someone qualified to do it. Planning around an assumption here is expensive, because discovering the problem at the visa stage leaves very few options.
Hypothetical example: A Canadian optical-lab owner considers an immigrant investor petition with a spouse, a twenty-year-old son, and an adult daughter. The first decision is who can be included as a derivative at the relevant stage, not who depends on the household financially. Spouses and unmarried children under twenty-one may qualify derivatively, while older children need another basis. Birth certificates, marriage records, passports, and any name-change documents should be collected early because the route moves through conditional residence rather than immediate permanence. The principal's capital must remain at risk and the project must satisfy the applicable job requirement; a family member's inclusion does not relax those obligations. The frequent planning error is treating a child's age as a background detail. Put each birthday on the timeline and obtain tailored advice where age protection rules may matter.