I'm trying to get some sites together with info for you with the help of a virtual friend, but in the meanwhile, better to have hurt feelings than a physically hurt daughter! Keep that kid away from her! Have her be conveniently "unavailable" for play time if you want to be vague. Or, if you want to be blunt so there's no mistaking your meaning, say, " I find the abusiveness of your son toward other living creatures startling, and do not wish for my daughter to think I condone that behavior by allowing her to keep company with him. Further, I don't wish her to become desensitized to any creature's suffering by repeatedly exposing her to it."