In this subchapter:
(1) "Child" and "minor" have the meanings assigned by Section 101.003, Family Code.
(2) "Missing child" means a child whose whereabouts are unknown to the legal custodian of the child and:
(A) the circumstances of whose absence indicate that the child did not voluntarily leave the care and control of the custodian and that the taking of the child was not authorized by law; or
(B) the child has engaged in conduct indicating a need for supervision under Section 51.03(b)(2), Family Code.