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In Missouri, if the parents can't reach a mutual agreement concerning custody of the children, the court shall determine custody based on the best interests of the child, considering all relevant factors including:
(1) The wishes of the parents concerning custody and the proposed parenting plan submitted by both parties;
(2) The needs of the child for a frequent, continuing and meaningful relationship with both parents and the ability and willingness of parents to actively involved in meeting the needs of the child;
(3) The relationship of the child with parents, siblings, and any other person who may significantly affect the child's best interests;
(4) Which parent is more likely to allow the child frequent, continuing and meaningful contact with the other parent;
(5) The adjustment of the child to the child's home, school, and community;
(6) The mental and physical health of all individuals involved, including any history of abuse of any individuals involved;
(7) The intention of either parent to relocate the principal residence of the child; and
(8) The wishes of a child as to the child's custodial parent.
When determining custody, there shall be no preference given to either parent in the awarding of custody because of that parent's age, sex, or financial status, nor because of the age or sex of the child.
[Based on Missouri Revised Statutes, Sections 452.375]
See link for child custody forms: http://www.courts.mo.gov/page.jsp?id=38352
It should have a form for you to file for custody. I would hire an attorney specializing in divorce or child custody and this will help you immensely in this situation as you will need to specialized knowledge of an attorney to give you the best chance for success.
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