The person has apparently had a sex change operation. Your child can tell the difference between a regular person and someone with a sex change operation? And then you're going to beat them up? Very strange.
There is more than one "transgendered" man/woman in my town, and they are simply men who dress and (try) to speak like women. They look like men in drag. Even hopefully not being able to see the mutilated genitals, my daughter would think that there is a man in the lady's room, a drunk one at that, and be scared. And if a drunk man dressed like a woman scares my daughter by being in the ladies' room at McDs, I'm not checking under the skirt before I look after my kid's best interests.
This said, I do not at all condone the brutality and I think the perpetrators should be arrested. It went far beyond getting a drunk man out of the ladies' room.