The parent who pays child support is in jail. Do they still have to pay?

Yes, even if one parent is in jail, they are still required to pay child support. However, it will be very difficult to collect child support unless that person has assets. The person in prison may file to amend the child support order, but if they fail to do so, past-due support will continue to accrue and that person will be required to pay the full amount when they are released.