This is not a "Family Law matter"-- such that CPS is not supposed to protect the children. There has to be more to this story.
All of Ms. Straus’ responses to questions posted on Avvo are intended as helpful information based upon the facts stated in the question, and are not to be relied upon as a final legal opinion. It may not be what you wished to hear, and it does not create an attorney-client relationship. Ms. Straus is licensed to practice law in California. If you would like to obtain specific legal advice about this issue, you must contact an attorney who is licensed to practice law in your state, and retain him or her. Me Straus provides “unbundled” services if you need specific assistance with a specific issue.
I recommend that you meet with the Family Law Facilitator at your Courthouse for free assistance in self-representation with full access to the Court's file for your case. It seems that either there is a lot more to this or the order needs to be updated to require Dad to ensure that Step Mom doesn't use corporal punishment. There should be a State agency to look into the care of your autistic son.