Japanese people have a hard time believing things that are new to them, and it's true for both adults and children. When I tell them that students in the US can actually be held back for poor performance and be forced to repeat a grade, they all say, "maji?!" And kids never believe me when they come looking for someone and I say, "Oh, I ate him. He was delicious."
Note: maji, or majide, comes from the base majime, which means serious.