Well it's pretty much an indication that something is wrong, first of all, remove the babies from the mother and start bottle feeding them.

 

According to the Merck Vet Manual, cannibalism often occurs from the mother's emotional stress (too much noise, overcrowding, over-handling of the kittens, constant interruptions, etc.)  This is the most common cause of such abnormal behavior.

Sometimes the mother will consume kittens because they are "constitutionally inferior" or malformed. It also tends to happen more with first time mothers. Although rare, a lack of milk, milk fever, hormonal imbalance, or breast or uterine infections may cause the same behavior.

Dee