Also, don't forget that if you are covered by a qualifying plan on December 1, 2021, you and your son can each make full year contributions for tax year 2020 ($8100 and $7100) under the "last month rule". You can make 2020 contributions up until April 15, 2021, as long as you tell the HSA bank that the contribution is designated for 2020 when you make the deposit.
