Well, it could have been because you're an idiot and kept both mum and dad together- once the doe is pregnant, you should put the buck in a separate cage until all the babies are weaned and given to different homes, then you can put the 'parents' back together again.
The mum probably felt threatened by the male and killed her babies to protect them, and the father probably attacked the babies- it's not like a human family group, they don't know about 'mum' and 'dad' and 'children'. They're just rabbits to them, and to a male rabbit, any other rabbit is a threat to his territory, his mate, and the food source, and must be eliminated- to the female rabbit who gave birth, the baby rabbits can be a burden, and if they're sick or she feels threatened, it's best to kill them.
And then they eat them so the smell of rotting bodies doesn't attract predators- it's how they clean the nest. What do you think they're going to do, have a little funeral?
If you're going to be irresponsible and backyard breed, learn more about it next time. NEVER keep the doe and buck together once she's pregnant, and NEVER put the buck in with her and the babies. End of.