(a) The following persons may execute an out-of-hospital DNR order on behalf of a minor:
(1) the minor's parents;
(2) the minor's legal guardian; or
(3) the minor's managing conservator.
(b) A person listed under Subsection (a) may not execute an out-of-hospital DNR order unless the minor has been diagnosed by a physician as suffering from a terminal or irreversible condition.