The spouse and unmarried children under twenty-one are admitted as dependants. The spouse is employment-authorized incident to status; the children may study but may not work.
One clear permission and one hard deadline
Hypothetical example: the technologist's wife works as an insurance adjuster and their son turns nineteen in the year of the move. She may accept employment in the United States because authorization flows from her dependent status itself, though any occupational licensing she needs is a separate state process with its own timetable. The son may attend school or college as a dependant but may not take a job, including a campus one, and his derivative status ends at twenty-one whatever he happens to be studying. Families frequently plan around a graduation date and miss the birthday entirely. Note also the interaction with the five-year specialized-knowledge limit: if the household expects to remain beyond that horizon, the route out should be identified at the beginning, since a child close to twenty-one has the shortest runway of anyone in the family.
Hypothetical example: a neon-sign repair company transfers its proprietary-controls specialist with a spouse and a child approaching twenty-one. The first review should create a date chart showing passports, relationship records, proposed activities, admission expiry, and the child's birthday. Those records resolve different questions and should not be inferred from a family surname. Plan any study, work, or independent status options before the age deadline. The frequent mistake is assuming that an assignment extension also extends a child's derivative eligibility, when L-1B's five-year cap and the family deadline may point in different directions.