Only a spouse and unmarried children under 21 may seek L2. In a household built over a long career, a child may already be over 21 or turn 21 during the assignment, and would need an independent basis to accompany or remain. Age at each step matters, so raise it early.
Check ages against the whole sequence
List every dependant with a birth date and compare it against the expected filing, visa, admission, and extension points, not only the first of these. A spouse in valid L-2S status is authorized to work incident to that status, and an employment authorization document is not universally required; a child in L2 is not work authorized. Where a child falls outside L2, plan that conversation separately.
Two dates matter more than the others: the day a child turns twenty-one, and the day the household's status would next need extending. Compare them, because a child who fits comfortably at first admission may not at a later step, and the alternatives are far easier to examine a year ahead than a month ahead. Where a child is already close to that threshold, treat their own basis for study or stay as a separate file from the beginning.
Hypothetical example: a rendering-plant process specialist's eldest child turns twenty-one eleven months after the intended start, so that conversation is scheduled with the initial review rather than at the extension.