L.,
I was a very dedicated dog owner before we had kids. We have two German Shepherds that were the focus of our lives. Sydney (11.5) and Raven (8) are still part of our lives, but on a much more limited basis. I know Sydney (my girl) wouldn't ever do anything to me or my DH and I trust her very much - with us. I don't feel the same with other people or especially with my boys. Raven wouldn't know how to hurt anyone, I don't think. Lol.
As for your son showing interest, my older son's first word was "GAH" which meant "dog". He LOVED watching our dogs and now our 6 month old just laughs and kicks when he sees them. I don't think you can really get your son to not be interested, so IMHO you should teach him how to respect the dog.
First of all, I'd teach your son to be gentle. I'd only allow him around your dog when it's a very controlled environment and you or you DH are there to control it. Show him how to pet the dog, "nice". At this point, we still don't allow our older son (2.5) alone with either of the dogs. He pets them, hugs them and they give him kisses - all when we're around and on a limited basis. Even Sydney, whom I worry about, lays on her back (a very vulnerable, trusting position for a dog) and wants belly rubs from our son.
Second, I wouldn't allow your son to chase the dog. That can be very intimidating for the dog and if he gets cornered very well could bite. If your son feels the need to chase (of course it's FUN!), then tell him that "Doggie will need to go away". Put the dog in a separate room for awhile. If he's running from your son, I'm sure he will welcome the alone time. :)
Dogs and kids can end up being the best of friends as long as boundries are clear and enforced. As much as I love my dogs, I never lost sight of what they are...dogs. They communicate with actions and actually give warnings before they haul off and bite. As humans, we just don't get their signals a lot of the time. By running away from your son, your dog is saying "leave me alone". Ignoring that could lead to a warning look, a lip curl, a growl and then a bite.
Good luck.
T.