A modest proposal:

If mothers made a habit of snacking on (each other's) litters of all sons, that would counteract the problem. That wouldn't require being able to differentiate among adult males, just between male and female children.

If the species takes a long time to wean children and doesn't reproduce until that process ends, this works better.

Mice, pigs, rabbits etc. (animals with large litters) already eat weak children fairly often, so this is somewhat plausible.