Think Longshadow probably has it right ... this is life in the wild. They're predators, so will eat a lot of other animals over their lives ... or else they'll be short lived. I think you captured Mother Nature doing what she does ... great shooting & thanks for sharing.
But they may be opportunistic about foxes that have died. These kits may merely be playing with a "prize," honing their survival skills. I've heard that cameras placed in fox dens reveal that even tiny babies are brutal towards one another, and that not all survive the attacks of their siblings.
You are close, let’s say, there were 7 Kits, there are now 5.....
Wow....I knew Eagle chicks were cannibals but I never suspected Fox Kits of the same behavior.That sure explains the history of some in my pasture that have suddenly thinned-out recently. Mange got one of them I know for sure . Thanks for the surprising heads-up.