"An action for child support (either an initial declaration or modification) must be brought in either the county where the parent or the child resides or in the county where the child is physically present."
I think this means that the papers must be registered here since this is where you and your children live. I’m not sure it can be registered in Fla.
"Absent an exception, child support terminates in North Carolina when a child reaches the age of eighteen. The two most important exceptions to this rule, for all orders entered on or after October 1, 1993, are that: 1) when a child is otherwise emancipated prior to age 18, payments terminate at that time, and 2) “[i]f the child is still in primary or secondary school when the child reaches 18, support payments shall continue until the child graduates, otherwise ceases to attend school on a regular basis, fails to make satisfactory academic progress towards graduation, or reaches age 20, whichever comes first, unless the court in its discretion orders that payments cease at age 18 or prior to high school graduation.” The other statutory exception to the rule against post-minority support applies to a child who is incapable of self-support. For such a child, the obligation of child support continues until the child is no longer physically or mentally incapable of supporting him- or herself."
This means that when you register it, your ex only has to pay until age 18 or graduating HIGH SCHOOL. If your child is still in high school until the age of 20 then the ex must pay until age 20 or graduation. If your child quits school, moves out on their own (emancipates), does not look like they are going to graduate before age 18 the ex can stop payments. In NC, unless there is a provision in the final agreement or court order for payments to continue after age 18 and graduation, the payments stop. If your court papers say “child support will be paid for the minor children”, then at 18 they are no longer minors. I’m not absolutely positive about this but I believe that since you never registered the papers, your ex was within his right to cut child support in 1/2 at age 18 of one child. If you register the papers, he may have to pay you back pay from when he cut the payments but only until the child graduates from high school.
Hopefully, an attorney will respond on this.