Many parents don't realize that they can be arrested and charged with kidnapping their own child. However, the law in California is very clear: If you withhold a child from his or her lawful custodian or legal guardian, that's a crime -- even if you are the child's biological parent. This is usually referred to as a "parental abduction."
It's also a crime to intentionally deprive the child's other parent of shared custody or visitation when he or she is entitled to it. This is usually known as "interference with child custody."