It probably is. The only disease that dogs and humans can pass back and forth through saliva is beta strep throat, which is rare. And if your son has a weakened immune system, you may want to be careful about exposing him to the normal bacteria that’s present in the saliva of healthy dogs.
Just a reminder since you have a child in the house, is careful your dog doesn’t become infected with worms. These parasites are not passed by saliva, but children can pick them up by playing on the ground or the floor.