Willow Rose Short had survived the transplant for two years before the family was found dead, all from gunshot wounds, on Saturday in their Sinking Spring home.
The grisly scene was discovered in the small town in Berks County on Winding Brook Drive in the Brookfield Manor subdivision, according to ABC 6.
The killings happened sometime on Saturday afternoon and the bodies of the parents and three children were discovered around 3pm, but it is unclear how.
The victims were identified as Mark Short, his wife, Megan, and their children Liana, Mark and Willow.
The other children's ages have not been released and police did not release who fired the fatal shots.
The Berks County District Attorney's office is leading an investigation into the deaths with assistance from police from Sinking Spring and Spring Township.