RSMo. § 452.375. 1.
As used in this chapter, unless the context clearly indicates otherwise:
(1) “Custody” means joint legal custody, sole legal custody, joint physical custody or sole physical custody or any combination thereof;
(2) “Joint legal custody” means that the parents share the decision-making rights, responsibilities, and authority relating to the health, education and welfare of the child, and, unless allocated, apportioned, or decreed, the parents shall confer with one another in the exercise of decision-making rights, responsibilities, and authority;
(3) “Joint physical custody” means an order awarding each of the parents significant, but not necessarily equal, periods of time during which a child resides with or is under the care and supervision of each of the parents. Joint physical custody shall be shared by the parents in such a way as to assure the child of frequent, continuing and meaningful contact with both parents;
(4) “Third-party custody” means a third party designated as a legal and physical custodian pursuant to subdivision (5) of subsection 5 of this section.
RSMo. § 451.375.5.
Prior to awarding the appropriate custody arrangement in the best interest of the child, the court shall consider each of the following as follows:
(1) Joint physical and joint legal custody to both parents, which shall not be denied solely for the reason that one parent opposes a joint physical and joint legal custody award. The residence of one of the parents shall be designated as the address of the child for mailing and educational purposes;
(2) Joint physical custody with one party granted sole legal custody. The residence of one of the parents shall be designated as the address of the child for mailing and educational purposes;
(3) Joint legal custody with one party granted sole physical custody;
(4) Sole custody to either parent; or
(5) Third-party custody or visitation:
(a) When the court finds that each parent is unfit, unsuitable, or unable to be a custodian, or the welfare of the child requires, and it is in the best interests of the child, then custody, temporary custody or visitation may be awarded to any other person or persons deemed by the court to be suitable and able to provide an adequate and stable environment for the child. Before the court awards custody, temporary custody or visitation to a third person under this subdivision, the court shall make that person a party to the action;
(b) Under the provisions of this subsection, any person may petition the court to intervene as a party in interest at any time as provided by supreme court rule.
2. Case Law Involving Individual Who Acted As Father For Child, But Turned Out Not To Be Biological Father:
In re T.Q.L., 386 S.W.3d 135 (Mo. 2012): “Petitioner’s third amended petition was sufficient to meet the requirements of section 452.375.5(5)(a) because it alleged the unfitness of Child’s biological parents and that awarding Petitioner custody of Child would be in Child’s best interest. In addition to Petitioner’s sufficient allegations of Mother’s and the unknown father’s unfitness, his petition to transfer custody survives a motion to dismiss because he alleges facts that the “welfare of 452.372.5(5)(a). This Court does not weigh the credibility and persuasiveness of the facts Petitioner alleged in his petition but acknowledges that those facts meet the elements of section 452.375.5(5)(a), and for that reason, the petition will be reinstated.”