The autopsy was conducted Tuesday.
Police say a 6-year-old playing with the gun fired the shot that hit Hoover.
The other boy's name has not been released, but the family says the two were cousins.
New Holland police are leading the investigation.
The Lancaster County District Attorney's Office and the Lancaster County Coroner's Office are also involved.
Information from: Intelligencer Journal, http://www.lancasteronline.com/pages/paper/sundaynews/