Let's say your son has the procedure in Oct. 2024 and you decide to open a FSA account for 2025. I am pretty sure you couldn't use the money you put into your 2025 account to pay for a 2024 treatment. You could use it to pay for the part of his treatments he receives in 2025 but that's it.
If you already had an FSA for this year, you would usually have a grace period into 2025 to get reimbursed for 2024 procedures, but it'd come out of your 2024 FSA allotment, not your 2025.
However, if the payment is going to be ongoing treatment and billed at regular intervals, you can pay for the 2025 work with your 2025 FSA. IA with OnAnAlanisJAG that it'd be worth it.
If you have any questions about the specifics, you should contact your HR or maybe even the orthodontist. In fact, you might be better off seeing if they could wait until Jan.
