"Our five-year-old often talks obsessively, and does not seem to listen when spoken to directly. What’s more, he seems to get easily distracted when doing the simplest task."
My advice is to take this little boy to a psychologist. This professional can determine if the boy maybe has an attention deficit disorder, is a gifted child... Or is simply a nervous person.
Another suggest for the parents is taking the boy to a library. In this quiet environment, reading books, paying attention to the librarian staff and his mates... He should learn when he can talk and when he can't. And finally, another interesting option for the child could be to play sports like football, handball, basketball or rugby. Maybe can be a good idea to try to focus his energy and efforts in a team game like these ones.