Inappropriate Play...working progress...

I have constant eyes on how Liam plays with Gwyn. I have a camera in his room that has a portable monitor so I can see what he is doing at all times. Now that Gwyn is older and into more things, I have to know what they are doing. Liam doesn't know how to play with Gwyn yet. His usual behavior with her is to get in her face and yell "aaahhh" in her face (like in this picture) and then flap his hands around. He doesn't know that he can't sit on her like a chair or step on her like a stool. He has no knowledge that he can hurt her and he doesn't care when she cries. AS children have no empathy for others and they fail to make the distinction between accidental and deliberate acts. When Gwyn touches his shoulder he yells at her and tells me "Tell her NO! She hit me!" I have to always remind him that it was an accident but he will repeat it over and over until you acknowledge his complaint and talk to Gwyn about not hitting. The one moment I didn't have an eye on them he ended up pushing her down and she bit straight through her lip, making a scar, all because she was touching his chair and that was the only way he knew to respond. He wasn't angry with her, he was just solving a problem. We are still working on this behavior just by reinforcing good behavior when he is being appropriate and letting him know when he is inappropriate. He gets a happy face token whenever he displays good behavior and if he collects 7 by the end of the week he gets to buy a car...his favorite "special interest".