How long can they keep you in jail for back child support?

My son was ordered to pay child support on a child he was not sure he fathered after we moved to Ga. After 7 years we were able to get a DNA test..the day they tell him he is the father they put him in jail for back support. He owes 9,000.he has paid while waiting for the DNA test...They told us he needs to pay 2000 to get out then in 30 days pay the remainder or back in jail? Is that legal? The state of idaho declared him the father by default whish we did not know there was a court date as we moved and he was under 18He was told 7 yrs ago she was not his but after moving to another state they deducted it from his wages but would not tell him where the child was to get a DNA.that is why it took 7 years to get the DNA. He has 2 small children at home can they legally keep him there??