However I have told her time and again that I don't want my kids within 1000 yards of this man. . . .
I don't really have any leverage here, and it is frustrating me. Legally I don't think I can do anything about her bringing our kids into contact with the OM. . . .
Any suggestions?
Are you sure of this? Have you talked with your atty about it?
TRO's are pretty standard stuff, and there may be a way you can get one against OM, even if you are separated. It's at LEAST worth looking into.
I myself was going to initiate such an action against my W during our divorce proceedings, when she was having here affair. Tactically, my atty advised doing it IMMEDIATELY AFTER the divorce decree, so as to not necessarily antagonize the opposition, and then of course the D never happened and my wife ended her affair, so it wasn't necessary.
They (Temporary Restraining Orders) are notoriously difficult to enforce, but it's worth looking into, if for no other reason than to let your wife know that you are serious, and stand ready to enforce your stated boundaries.