A police spokesman said the child is in serious condition at a hospital in London.
Before noon on Friday, police blocked off a section of Church and Erie streets, where the incident apparently happened.
Sgt. Matt D'Asti of the Windsor Police Service said the boy was walking by the suspect's house when the alleged attack happened.He said the boy lived down the street from where the attack took place.
"This easily could have been, you know, much worse. We still don't know the exact extent of the injuries to this young boy. The latest we've heard is that his condition is serious. We know that he has multiple skull fractures and we know that his injuries are serious enough to have him transported to London," said D'Asti.
D'Asti said the boy was off school for a PA Day, but that police are not aware of any conversation that may have taken place between the victim and the suspect, or whether the two knew each other.
Police have arrested a 28-year-old man and the incident is being investigated by major crimes detectives.