Child Custody, Race, Religion, Morality and Lifestyle Preference, Consideration

At times, they go as far as to invoke the moral fitness, lifestyle, race, and religious preference of a parent to determine legal and physical custody. What is does “The Child’s Best Interests” Really Mean? Can a court consider a parent’s Race, Religion, morality, live style preferences? Which test is appropriate, the ” Per se” or the “Nexus” Test to determine custody and when?