A legally married spouse holds L-2 status and is employment-authorized incident to that status, so a second career need not be paused. Unmarried children under twenty-one accompany as derivatives and attend school, but they hold no work authorization and lose derivative eligibility at that birthday.
Plan the second career and the twenty-first birthday together
Because the L-2 spouse may work incident to status, a two-year posting is less disruptive for a dual-income household than derivative status under some other categories would be. That advantage is worth stating plainly to a spouse who has been assuming a career interruption. The planning still has edges.
A common-law partner is not a spouse for derivative purposes and needs an independent basis to accompany him, which takes lead time and should not be left until the posting is announced. A child who turns twenty-one during the assignment stops qualifying as a derivative on that date, and the alternative for that young adult, usually a student route, has to be arranged before it happens rather than afterwards. Schooling for younger children proceeds normally.
Health coverage, driver licensing and the tax treatment of the spouse's American earnings are separate questions that the family should put to the appropriate advisers early, since none of them follow automatically from the immigration classification.