Only if he is under twenty-one and unmarried can he be admitted as a dependant at all, and dependent children have no work authorization. An adult son would need his own basis to be in the United States and his own authorization to work there.
Children are dependants for permission, never for payroll
Derivative status under E-2 covers the investor's spouse and unmarried children under twenty-one. The spouse is employment-authorized incident to status and can work anywhere, including in the family business. Children can be admitted and may attend school, but the classification gives them no ability to work, so a nineteen-year-old cannot be put on the facility's payroll or paid cash for weekend shifts, and doing so is unauthorized employment on his side.
Once he turns twenty-one he is no longer a derivative at all and needs an independent reason to remain. Families running a small business find this counterintuitive, because the work is at home and informal. The safe rule is that only the two adults who hold work permission may perform services for the business.
If the son's labour is genuinely needed, the answer is a paid employee, which incidentally helps the marginality analysis. Hypothetical example: a Hope optician and spouse buy a U.S. eyewear boutique, and their twenty-year-old daughter wants to manage the store’s social-media account for spending money.
The first review separates a child’s ability to attend school from authority to provide productive services. Her age and family record settle derivative eligibility, but no informal role becomes permitted because it is online or unpaid. The parents should choose between hiring an authorized worker and keeping the account under an adult who may work.
They should also plan for an independent status route before the daughter reaches the derivative age limit.