Child custody cases in California are generally guided by the principle of the "best interests of the children," which is the universal test used by state courts throughout the country. More specifically, however, child custody courts will look to a number of factors to determine custody in a contested case. The courts will try to find the factors that are important to the facts of the case to bring about a decision that reflects the best interests of the children.
For example, the courts will look to the respective homes and living conditions of the parents or, in some cases, of a parent as compared with those offered by the grandparents. The quality of the homes, the facilities, the resources and the amount of space available are practical measures that are examined. The preferences of the children are also considered, but this factor is more influential for older children.
In those cases, the family law judge brings the children into chambers and questions them on their home life, their relationships with each parent and which living condition would be most satisfying for the child. Where the parents live in close proximity to each other, the court will be free to choose a joint custody arrangement which stresses a 50-50 sharing of the time that each parent spends with the children. Where that is not feasible due to distances, the court may gravitate toward a decision that awards primary physical custody to one parent with reasonable visitation privileges to the other.
The preferred arrangement theoretically in California and many states is called shared custody. That arrangement attempts to share the parents' time fairly equally with the children, but is most concerned with setting up a system in which the parents perform the parenting responsibilities together and equally. This is the system that is favored by most experts who have studied the phenomenon of child custody living arrangements. They have found that children who develop a close working relationship with both parents are healthier and better behaved as they grow up.
Source: wisegeek.com, "What Factors Influence Child Custody Cases? (with pictures)", Lori Smith, Nov. 7, 2017