from IRS PUB 969 on HSAs
Family HDHP coverage is HDHP coverage for an eligible individual and at least one other
individual (whether or not that individual is an eligible individual).
The amount you or any other person can contribute to your HSA depends on the type of HDHP coverage you
have, your age, the date you become an eligible individual, and the date you cease to be an eligible individual. If you have family HDHP coverage, you can contribute up to $7,300 (2022)
the HDHP coverage must either exist on the first day of each month or under the last month rule (LMR) on 12/1/2022. The LMR requires you continue HDHP coverage through the end of 2023
so you must have a family HDHP that covers you and your child for the maximum contribution
