If you are in prison, your obligation to pay chld support does NOT go away.
The amount you owe will continue to add up and you will be charged interest (6%) on any unpaid child support.
Eventually, you will be paying interest on interest.
If you have the ability to pay child support while in prison (savings or investments, etc.) it is in your best interest to pay your child support.
You can request a modification to your child support due to incarceration, but the judge is not obligated to reduce your child support.