Only a spouse and unmarried children under 21 can be included as accompanying family, each with their own processing fee and gift per the official page. A 22-year-old is not a derivative and would need a route of their own.
What usually goes wrong
Households routinely budget for the principal and assume the family follows at no extra cost, or assume that every child follows regardless of age. Neither is what the official page says. Hypothetical example: a Lévis shipyard executive plans for herself, her husband, a nineteen-year-old in college and a 22-year-old working in Montréal.
The nineteen-year-old may be included, with his own fee and gift, but if processing runs past his twenty-first birthday his inclusion needs to be reassessed, and the Child Status Protection Act's treatment of this framework should be confirmed with counsel rather than assumed. The 22-year-old cannot be included at all. Her plan therefore covers three people with a question mark over one, and a separate conversation about the eldest.
Build the family total from the official per-person figures on the day of decision, verify the terms before payment, and record each birth date against the processing estimate.