When my boys were 3 and 5 it was discovered that their father was leading a double life. He disappeared. I was granted custody, his rights were not revoked, but child support was left open, to be determined... because he could not be found. My youngest has just turned 18 and their dad has surfaced. Can I take him to court to get back child support?

So the court never determined an amount to be paid in support? If that's the case, how would he know how much to pay for back child support? Also, the child is now an adult.

I'm not a legal expert, but from what I've read in similar questions on this site, it's unlikely that you'll get back support.

If the court order was filed and ruled on, So it will depend on the exact disposition of the case. You can file for the back support that was due from the original order, not file a new order

So without knowing the exact situation with the first court order, you will need to have a local attorney review it.

Agreed, it depends on the wording of the original order. You need to go back to court to see if the original order can be enforced. It's possible, based on what you said, but not a sure thing.