Behavior patterns for the young can be different from those for adults. This type of thing isn’t unprecedented in real r-strategy (or semi-r-strategy) species. Sharks, for example, eat each other in the womb, but that isn’t normal for the adults.
In fiction, similar behavior is used by the Prador in Neal Asher’s Polity books, the Martians in Stranger in a Strange Land, and Harry’s species in Resident Alien, for example.