I thought of a brood parasite that co-existed with humans and has evolved to mimic humans and to infiltrate human families as a brood parasite -- similar to a cuckoo birds -- as adopted children who are placed by this species in adoption centers or dropped of at front doors as babies.
Its lifecycle: After infiltrating a family, it would eat as much food as its fake human parents can get, and this species is sapient and intelligent so they would learn their parents' language and mimic what they do to help integrate itself into human society. Also, in another thing similar, to the cuckoo bird, it will try to kill off any siblings and un-necessary family members through (accidents supposedly) to prevent any food and attention heading for other people. After it reaches adulthood and its fake human parents becoming a liability, it would collect as much food and abandon them and survive off foraging, hunting, you name it and repeats the cycle.
Is this species plausible or not and if not why?