Each accompanying spouse and each unmarried child under twenty-one attracts a further processing fee and a further one million dollar gift. A child of twenty-one or older is not covered as an accompanying child and would need a route of their own, so household arithmetic changes sharply with a birthday.
Count the household before quoting the household a figure
The family provisions are additive rather than inclusive, which is the opposite of what people assume from other categories where dependants are covered by the principal's filing. Each qualifying person carries the fee and the gift again. Age is therefore not only a legal question but a financial one, and it is fixed: unmarried and under twenty-one is the boundary, with no allowance for a young person still in full-time study.
A household with children on either side of that line should map the numbers for each person separately before treating any total as reliable. Hypothetical example: a maker of bee-hive equipment budgets for himself, his wife and both children, aged seventeen and twenty-two; the elder is outside the accompanying-child definition entirely, and the family's real question about him is which independent route exists rather than what he adds to the total. The arithmetic should be done person by person and written out before any total is quoted to the household.