Yes, the use of the medical plan card you described would be fraud.Fraud is the intentional misrepresentation of a material fact made with knowledge of its falsity and with the intent to induce reliance upon which one justifiably relies to their detriment. The insurance plan card is being used with knowledge that the medical plan is no longer in effect in order to induce the medical provider to rely on it for payment which the medical provider justifiably does to its detriment.Fraud is both civil and criminal.  The mother of your children could be sued for fraud (civil case) and criminal charges could be filed in a separate criminal case.