putting it in other words, they still have uncorrupted moral compass since they are still kids. no hypocrisy like the adults.
yes, they lived a super happy life, but in a super special environment where the children is raised to be as intelligent as possible, including all the practical ability on top of their hardcore every-morning written test. And, dont underestimated books, not all books are text book, they had access to fictional, history, and conspiracy book too.. we have 3 main chara here that are the top 3 meat, even their meat were only meant to be served to ¢¥π•÷. And those smartest human in demon world are shaping the story with their uncorrupted morals (i don't know about Norman though..)
These guys may be super duper smart but they're still children. Not to mention they only lived a super happy life in a orphanage and then a super devastating one where everyone is dying.
They're basically just book smart. Lots of trivia in their heads but don't know how to make life decisions. They also didn't have parents, just a nanny that didn't need to teach them life stuff cuz they were meant to be food.