I believe they should have asked permission, but I don’t believe you have any recourse. Your son did this voluntarily. You let him go. They didn’t do anything that would endanger him. The courts don’t like cases based on religion and usually find any way they can to dismiss them.
This reply is provided for information purposes only and does not represent legal advice or an attorney-client relationship.
Unauthorized baptism can generate considerable anxiety in the mind of the parent who believes their will was thwarted. But unless they dragged him to the baptism against his will and thereby comitted any torts such as false imprisonment, assault, or battery, you have no legal recourse. The law does not recognize baptism, so the law has no remedy for unwanted baptism.
If you are a believer of any type, I would suggest you take your son to church, etc. with you and not let him go with others. If you are not a believer of any type, then don't let your son go to church if you think it will bring him harm. But if you let him go with others, you need to find peace in the notion that he will partake of their sacriments and subscribe to their beliefs.