Child support orders require periodic payments. This generally means that each installment can be deemed a separate order or judgment with, depending on state law, the limitations period starting on that date. But it is possible that at one point in time or another a court will enter a new order or judgment restating the total arrearage owed, with the limitations period running from that date - the date the arrearage is reduced to a judgment.
NCP had a CS order, fell into arrears.
Several years later NCP filed to modify due to eldest child aging out. Order was modified, with no mention of arrears owed.
5 months after the modification the CSE filed a petition for payment of arrears, in a seperate order the amount of arrears was determined with periodic payments ordered. This was a completely seperate order from the CS order and did not mention the on-going CS (same case number though).
In a situation like that, does it mean that the seperate order reduced arrears to a judgement?
Yes, based on what you have stated, I would describe that new order as reducing the arrears to a judgment.