[JoeyP]

One thing is never Ever leave your dog within reach of the baby

But you can at least have them in the same room by holding the baby
and do not look at the dog at first
walk around the room with him in your arms and drop treats every once in a while for the dog
The dog is going to be occupied by the treats and will not be after your grandson
Next step is have the child in the room in something like a playpen where the dog cannot get to him
let the dog come in
If he barks or tries to get to the baby ... he is put out
wait a few mins and repeat the process
You need to make the dog realize that good things will happen when the baby is around