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?
Take her to the vet!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Goodluck.
Vet immediately