As I see it, the CM was defending a major and sacred asset of the Disney Company and should receive a promotion. I would imagine that CMs are literally blind-sided while in one of those costumes and when the CM felt someone tampering with his costume, he turned to protect it and, in doing so, accidentally brushed the boy's face. I also have to imagine that removal of part of the costume while in a guest area, intentionally or otherwise, must be a mortal sin to the Disney Company and part of the inculcation provided to the employees.
The CM's job and reputation are on the line and, unless he just decided to belt this kid for the hell of it, he's the only party that has been damaged in this incident. I feel real bad for this guy for being put in an untenable situation.. We can all make claims about how he could've reacted or how we would've reacted but, truth be told, he acted with a great deal of restraint and prudence considering the consequences if that kid was somehow able to unzip the skin or tip the costume head off the CM.