Everyone seems to be at fault here, besides OP who was not there.
Your dog causes damage, it should be put down. If my Chi mauled a baby, regardless of how I have never been able to get her to bite me while rough-housing, regardless of the fact she is the sweetest most obedient dog I have ever met (I love animals, have met a ton), she should be put down. If she bites my ten month old baby boy tomorrow, I would turn her over to the county. (tear) Same goes for my cats, and I like them better than my dog. My pets are family to me, my wife, well she does not think of them that way.
OP my biggest wish for you is that your son comes out of this unscathed, my heart literally sank when I read your first post.