Tex. Insurance Code § 1251.154

A group policy or contract of insurance for hospital, surgical, or medical expenses incurred as a result of accident or sickness, including a group contract issued by a group hospital service corporation, that provides coverage for the immediate family or a child of an insured may not exclude from coverage or limit coverage of a child of the insured solely because the child is adopted. A child is considered to be the child of an insured if the insured is a party to a suit in which the insured seeks to adopt the child.