I am assuming that your Husband agreed to her proposal and his son has lived with him and his daughter has lived with is ex-wife.
Every state has child support guidelines, but each state uses a different standard set by their legislature. If child support and the arrearage was calculated based on California law, I cannot tell you if they took into account the fact that he had another child or not.
I think there are facts that I am missing here. Did he attend the hearing for child support in California? Did he tell them at that time that he had a child from the same relationship that was living with him? Because it has been over four years from the time that this order was entered, it is unlikely that he will be able to modify the arrearage amount at this point.
NC is not getting more involved because KY still has jurisdiction over the child support issue and only one state is going to take jurisdiction of this at a time. Your Husband may want to consult an attorney in KY to see what his legal options are, but in order to modify the order related to his son, he will need to travel to KY for the hearing, he needs to be there to give evidence.
Helena M. Nevicosi
Attorney with Rosen Law Firm
4101 Lake Boone Trail, Suite 500
Raleigh, North Carolina 27607
919.787.6668 main phone
919.787.6361 main fax
301 McCullough Drive
Charlotte, NC 28262
Main Phone: (704)307.4600
Main Fax: (704) 9343.0044
Durham & Chapel Hill Office
1829 East Franklin Street
Chapel Hill, NC 27514
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