Set in the year 2045, Emma is an 11-year-old orphan living in Grace Field House, a self-contained orphanage housing her and 37 other orphans. Life has never been better: with gourmet food; plush beds; clean clothes; games; and the love from their “Mom”, the caretaker, Isabella. The bright and cheerful Emma always aces the regular exams with her two best friends, Ray and Norman. The orphans are allowed complete freedom, except to venture beyond the grounds or the gate, which connects the house to the outside world.
One night, an orphan named Conny is sent away to be adopted, but Emma and Norman follow her after noticing that she left her stuffed toy, Little Bunny, back at the house. At the gate, they find Conny dead, and they realize the truth of their existence in this idyllic orphanage—to be raised, eventually butchered, and sold as meat to a species known as demons. Determined to break out of Grace Field House, Norman and Emma join with Ray to find a way to escape along with their other siblings.
–From Wikipedia
The story begins as Emma and Norman realize that their "orphanage" is, in fact, a farm in which the children within are raised as livestock for creatures known as "demons" https://yakusokunoneverland.fandom.com/wiki/Story_Arcs
Promised Neverland