I cannot claim my children on my taxes, but have joint custody with my ex-wife. Am I allowed to use my HSA to pay my children's medical expenses and be reimbursed?

My ex-wife remarried, claims our children on taxes, but I have joint custody with her. I could claim them if she didn't, so can I still pay for their medical expenses using my HSA until they are adults or was that only for 6mos after the divorce?