Unmarried children under twenty-one may accompany the transferee in dependent status and may attend school, but they may not work. Dependent eligibility ends at the twenty-first birthday, which for a five-year assignment often falls part-way through, so an older teenager needs a plan before that date rather than after it.
The birthday is the deadline nobody diarises
Households plan around the principal's dates and rarely around the children's. The rule is simple: a child qualifies as a dependant while unmarried and under twenty-one, and on that birthday the derivative eligibility ends regardless of what the principal's status permits. A young person continuing studies then needs a status of their own, which takes months to arrange and depends on an admission decision by a school.
The other half of the household usually has better news, since a spouse in this dependent status is employment-authorized incident to status without a separate permit. Hypothetical example: an irrigation-controls specialist transfers with a spouse who holds a Quebec pharmacy licence; her right to work is not the obstacle, but practising pharmacy in that state requires that state board's own licensure, which is a professional question no immigration approval answers. Licensing enquiries belong with the state board directly and early, since recognition of a Canadian qualification varies widely between jurisdictions.