Baby and Dog

Need some advice...

My SIL has a bulldog/Labrador mix who they claim is only “dog aggressive.” This dog tried to kill my dog one Thanksgiving. My SIL and BIL acknowledge that the dog is “dog aggressive,” but still take it to dog parks and outdoor restaurants and have even had to break up public fights that this dog has instigated.

My son is 7 months old, and even though they say their dog is only “dog aggressive,” I don’t want my baby to be around this dog during the holidays. My husband’s family is planning on having Thanksgiving at his house, and of course his sister plans on bringing her dog. My son is the first grandchild and so everyone is excited to see him for the holidays. But I refuse to bring my son (who will probably be more mobile) around this dog. How do I broach this subject with my SIL and in laws? I hate to tell my SIL she can’t bring her dog to her own parents’ house for the holidays. But I will not have my son around this aggressive dog.