This is prey drive, and likely will not affect your son in the least.
HOWEVER.
If you haven’t yet, I would invest in a crate. Train the dog to accept the crate, and crate the dog when you cannot supervise. Had the dog been tested around cats prior to moving him to your home?
He does kind of have a bully-type head. But I am really not good at guessing breeds.
Looks like a mix to me. Does he talk a lot? Is he stubborn? Is he totally devoted to you, or is he aloof?
For $70 you may be able to get a better answer than we can provide looking at a photo. Mars Wisdom Panel is a DNA test that I have found to give very good information on my own dogs, and dogs I have fostered. But, the more mix your dog is, the less satisfying the results of the test. I get mine from Amazon – look for the 2.5 or 3.0 version, they are the newest and give more info than earlier versions.
I have tested 5 dogs so far, and have been delighted with the results.