Unmarried children under 21 may seek L-2 status as dependants, but that status does not authorize employment for them. Their position is therefore a schooling and care question rather than an income one, and childcare cost may be what decides whether pursuing the second income is worthwhile.
Cost the care arrangements honestly
Compare expected earnings with the actual care arrangements the household needs, including any school-age or younger children. Add school enrolment timing, a later arrival for part of the family and any child approaching 21 to the plan. Do not assume either partner can provide care during working hours.
These are household choices to assess alongside each person’s immigration dates, not conditions that establish dependent eligibility. Work out the childcare figure before deciding whether the second income is worth pursuing, since in some households it is not, at least in the first year. Compare expected net earnings against full-cost care for each child who needs it, add commuting and any period before a school place is available, and look at what remains.
That calculation sometimes supports a different plan altogether, such as the spouse taking the first months to settle the household and beginning work at the start of a school year, which is a legitimate choice rather than a concession.