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.
A post-mortem on a Gloucestershire man who was found dead with his three children has established he fell from height.
Flowers and teddy bears have been left in tribute at the children's school
Three Gloucestershire children were discovered dead with their father near Shrewsbury yesterday