I agree. Keep them apart until he is old enough to understand. It's not fair to either one of them to keep putting them in that situation
Immediate physical separation when it does occur. Not just hands moving away, our entire bodies. We’d only give a dog one opportunity to be rough with a child, why should we give children multiple opportunities to be rough with a dog? Explain that it is not a game, that dogs are beings with feelings, and beings with sharp teeth. If you don’t respect their space & feelings, you might get hurt.
You’re going to need to keep them apart if he can’t stop annoying the dog because one day that dog is going to snap. I was that age when my dog bit me on the face because I was pulling his tail, not worth the risk in my opinion!