Detective Chief Inspector Neil Jamieson from West Mercia police said a Home Office pathologist conducted post mortems on the children yesterday afternoon.
The examinations established that Sam Fuller, 12, and his sisters Rebecca, 8, and Charlotte, 7, all died from stab injuries.
A post mortem has yet to be carried out on their father, 35-year-old Ceri Fuller, who was also found dead in the former quarry near Shrewsbury on Monday morning. This is expected to be held later today.
Formal identification of all four is expected to be take place tomorrow.