The six-year-old, who has not been named, died at Alder Hey Children's Hospital in Liverpool after being rushed there following the incident.
An eyewitness, who was in his car when the tragic collision, occurred told the Liverpool Echo: "I was in the traffic when I heard screaming, I looked in my rear view mirror and I could see a child laying in the road.
"People were screaming and panicking so I pulled over and dialled for an ambulance.
"It was awful, my heart goes out to his parents."
The driver of the van was taken to hospital as a precaution.
Police shut the road for several hours while they carried out their investigations.
The six-year-old's grandfather Richard Williams died on August 14 after being discovered unconscious with serious injuries near the club he owned.
A man has been charged with the 64-year-old's murder and is due in court in November.
A Merseyside Police spokesman said: "Specifically trained family liaison officers are supporting the boy's family at this difficult time and an investigation into the full circumstances surrounding the incident is continuing.
"Anyone who witnessed the collision is asked to call officers from the MSOC Roads Policing Unit on 0151 777 5747."
