A taxpayer marries during the year and has a workplace$-$provided health insurance plan which is reported to him on a Form $1095-$B$.$ His new wife and children were added to his policy part$-$way through the year. The children originally had coverage through their biological father, who was on a healthcare plan through the marketplace. The IRS sends a notice to them after filing saying that they need to fix their return related to the healthcare. What is the likely reason?