One woman was there because she gave her misbehaving kid a severe spanking, and the kid complained to school authorities. The school had to turn her into CPS, which is now called Child Welfare Services in California. They changed the name to emphasize that they are no longer focused on protecting children.
She said that the police and CPS explained to her that she can spank her kid as long as she does not leave a mark. She can even use a belt on a bare butt, as long as it does not leave a mark. California law says that it is a crime to spank and leave a mark.
In the case of this woman, no one ever saw a mark on the kid, but the mom did not deny the possibility that a belt might have left a mark for a few hours. So they took away her kid and sent her to a parenting class.
I checked the law:
A corollary to this fundamental principle is that parents have broad discretion in the disciplining of their children and are allowed to use corporal punishment. Under California state law, a parent has the right to reasonably discipline a child by physical punishment and may administer reasonable punishment without being liable for battery. People v. Whitehurst, 9 Cal.App.4th 1045, 1050 (1992). In order to be considered disciplinary the punishment must be necessary (i.e. there must be behavior by the child deserving punishment), and the punishment must be reasonable (i.e not excessive). Id. It is important to remember that the reasonableness of the punishment will be judged by a third party and it does not matter if the parent believes the punishment was reasonable.So there is really nothing in the law about leaving a mark. According to my source, the police and CPS pay no attention to what the kid did to deserve a spanking or anything like that. All they look at is whether the punishment left a mark.