The legal standard in deciding who will get custody is what is in the best interest of the children. Every judge sees it differently. If the judge’s father abandoned his family and the judge’s mother slaved day and night to help her son through law school, then the judge will have a hard time understanding why a father should have custody. The mother does not have an automatic edge in litigation. The fathers win in at least half of the litigated cases.
There are also certain doctrines and presumptions (but not inflexible rules or requirements) which aid the court in determining the best interest of the child:
Parental rights, Parents must be shown to be unfit before the children will be given to someone else, such as grandparents.
Continuity of placement. If children are doing well where they are, do not mess things up by moving them.
Children’s preference. A judge will consider who the children want to live with. The judge may talk to the child in private and may talk to a child younger than fourteen years of age. The judge is not bound by what the child wants.
Other. The court can consider the custodian’s age, health, wealth, religious beliefs, conduct, type of home, psychological evaluations; the location of the residences of the child’s siblings; the child’s school performance; or anything else the court considers important.