Is a request for Child Support valid if 100% custody was given to the ex-husband?

My wife divorced her ex-husband some +12 years and we have been married for 7 years. About 1 year ago the ex-husband filed for 100% custody of both children and through mediation my wife relinquished full custody to her ex. My wife has had very little contact with the two kids and is not part of their lives. The ex and the kids live in California and we live in Illinois. We just received an "Order to show cause for Child Support" and we were under the impression that since she relinquished full custody of the kids to her ex that Child Support could not be requested. Additionally, since we are married and as the husband and no relation to the kids does my income have to be included in the Form FL-150 (Income and Expense Declaration). My wife does not work and I am her sole provider