Missouri Revised Statutes Title XXVIII. Contracts and Contractual Relations § 431.065. Minor spouse or parent may give consent, when

Any minor who has been lawfully married and any minor parent or legal custodian of a child, if otherwise competent to contract, shall be considered an adult for the purpose of entering into a contract for surgical, medical, or other treatment or procedures for himself, his spouse, his child and any child in his legal custody.