The spouse and unmarried children under twenty-one are derivative beneficiaries and obtain conditional permanent residence alongside the investor. The risk is that a child turns twenty-one during a process measured in years. Statutory protection can freeze a child's age for part of the time a petition is pending, but it does not cover every delay.
Count the child's age in months, not in years
Nothing in this route is quick, and the interval between filing and residence is precisely the interval in which a teenager stops being a child for these purposes. The age calculation is not simply the birthday: part of the time a petition sits with the government can be subtracted, and the family must then act within a set period once a visa becomes available. What the calculation cannot absorb is a family's own hesitation later on.
Hypothetical example: the eldest child of an investor from Sainte-Cécile-de-Milton is twenty years and four months old when the petition is filed. Every subsequent decision, including whether to consular process or to adjust status and how promptly the family responds to requests, may affect whether she is included. Her position should be calculated at the outset and rechecked at each stage, and a separate route should be considered in parallel rather than assumed to be unnecessary.