Language provides an intermediate step between the stimulus and the response.
When language is acquired, it becomes an intermediate step that can delay and/or change the response.
Hence, Edward with language may still want the doll but will think to himself linguistically, "The doll does not belong to me. Teacher has said that it is wrong to take some thing that does not belong to me."
Then he would probably take the doll anyway, but it would take him a little longer to commit the crime than it would have without language. And who knows, he may even feel some guilt. The point is that non verbal kids are impulsive and hard to control in and out of the classroom.
My conclusion then, from what Vygotsky has theorized, is that we need to be as aggressive as we know how in our strategies to facilitate the development of speech during these formative years, before the internalization process concludes.