M.S.A. § 518.17. Custody and support of children on judgment
Subdivision 1. The best interests of the child. (a) "The best interests of the child" means all relevant factors to be considered and evaluated by the court including:
(1) the wishes of the child's parent or parents as to custody;
(2) the reasonable preference of the child, if the court deems the child to be of sufficient age to express preference;
(3) the child's primary caretaker;
(4) the intimacy of the relationship between each parent and the child;
(5) the interaction and interrelationship of the child with a parent or parents, siblings, and any other person who may significantly affect the child's best interests;
(6) the child's adjustment to home, school, and community;
(7) the length of time the child has lived in a stable, satisfactory environment and the desirability of maintaining continuity;
(8) the permanence, as a family unit, of the existing or proposed custodial home;
(9) the mental and physical health of all individuals involved; except that a disability, as defined in section 363.01, of a proposed custodian or the child shall not be determinative of the custody of the child, unless the proposed custodial arrangement is not in the best interest of the child;
(10) the capacity and disposition of the parties to give the child love, affection, and guidance, and to continue educating and raising the child in the child's culture and religion or creed, if any;
(11) the child's cultural background;
(12) the effect on the child of the actions of an abuser, if related to domestic abuse, as defined in section 518B.01, that has occurred between the parents or between a parent and another individual, whether or not the individual alleged to have committed domestic abuse is or ever was a family or household member of the parent; and
(13) except in cases in which a finding of domestic abuse as defined in section 518B.01 has been made, the disposition of each parent to encourage and permit frequent and continuing contact by the other parent with the child. The court may not use one factor to the exclusion of all others. The primary caretaker factor may not be used as a presumption in determining the best interests of the child. The court must make detailed findings on each of the factors and explain how the factors led to its conclusions and to the determination of the best interests of the child.
(b) The court shall not consider conduct of a proposed custodian that does not affect the custodian's relationship to the child.
In Minnesota, most of these situations are resolved prior to a trial with a guardian ad litem/custody evaluator peforming a custody investigation based upon these factors and making a recommendation to the court. Works pretty well.
Regarding visitation, I have conflicting thoughts. While I know how important it is for a child to have both parents present in their life, for many reasons not the least being so the child knows their parent loves them and they are not rejected, many cases of visitation disputes I'm involved in occur because the younger child typically will not want to leave the parent they're with, and when they do go visit the other parent, the first few days after visitation are spent "coming down" from the visit. I absolutley believe that a 50-50 split (alternating weeks being the most popular) is not at all good for children. They have no stability in their home, which is very important, and their bonding with both parents suffers. It's a problem with no solution, I fear, other than parents being able to stay together. That's why that recent study which stated that children are better off in homes with troubled marriages than being in tranquil homes with a divorced parent.