OM has no business administering any sort of corporal punishment to your children. Find a good lawyer as fast as you can. You might also consider contacting Child Protective Services (don't know what it is called in Texas), but I would get legal advice first.
In a perfect world, you could go kick the guy's a$$ for even touching your son. In the real world, that would be used against you in a custody dispute.
If your wife is turning over the discipline of your children to Mr. New Guy because she can't handle it herself, perhaps she is not fit to have custody. Those are your children, and you have the right and responsibility to expect and demand that they be treated appropriately--even if it does result in hard feelings. Just make sure you do it through legal channels to assure that your rights are not jeopardized.
