Jaws 3 in 3D featured a baby great white frolicking and feeding at Sea World, followed of course by attacks that could not have been carried out by the baby, leading in turn to the obligatory revelation from an expert that young that size must have a mother shark who has given birth to it in close proximity and is responsible for the attacks.

What about the situation in which the hero kills the monster, and only then find she was a mom. Adopting the monsterling is optional (why there's never a Sociopathic Anti Hero who kills the monsterling in this situations?).