Jeepers the Prostitute comment, what on earth!!!
Is it not more likely that Harvey has some type of GDD diagnosis rather than his development being hindered by her, of course I'm sure her parenting has not helped nor has the chaotic environment he's living in. I know disabled adults who love Mr Tumble etc, they live in supported housing and appear to have a little more independence than Harvey.
I think that the therapy he had whilst in LA in his youth really helped him, I recently saw one of his consultants saying they couldn't believe his development and they never expected him to do x y or z, this was from one of the TV shows way way back. Unfortunately for Harvey he isn't his mother's top priority, unless its for views/content.