Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
I am so sorry to hear about your situation with Boo Boo. YOu were so kind to take him in and there are ways to help Boo Boo past this. Abused dogs have a hard time trusting and when a baby is introduced, this makes it even harder for him.
This is a common problem with rescue dogs. The best thing to try is an ultrasonic collar. Use it when you are present and it sends a high pitched signal that the dog dislikes and will discourage this behavior. I have also had very good results with the collar combined with a drug called Reconcile. I have also had good results combining Reconcile with a DAP Collar, available at the pet store. This is a canine pheromone that acts as a calming agent. Reconcile or Fluoxetine is a prescription medication that acts as a calming agent and will, along with the collar, retrain your dog so the aggression is minimized. I know this sounds severe but this is a very serious situation and you do not want to put your family or others at risk. Call your vet about this product. The package insert will have behavioral modification techniques that will help.
It is also recommended that you have your vet examine Boo Boo to be sure there is not a medical reason for this change in behavior.
Here is a website that has more information that might be useful for you: LINK
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, ***** *****