Despite their young age, children can have very profound thoughts - as one pupil has proved.
Teacher Bret Turner, from Albany, California, explained how one of his first-graders (aged 5 to 7) had given the philosophical answer "death" to his tricky puzzle of the week - causing an "awed, somber [and] reflective hush" to fall across the room, the Daily Mail reported.
The riddle read: "I am the beginning of everything, the end of everywhere. I'm the beginning of eternity, the end of time & space. What am I?"
Bret explained how the first guess from one of his pupils was "death", and others included "all stuff", "the end" and "nothingthing".
He said that when he finally revealed the correct answer - the letter e - the class of pupils were "largely unimpressed".
Sharing the puzzle on Twitter, the teacher explained: "The first guess from one of my 1st graders was 'death' and such an awed, somber, reflective hush fell over the class that I didn't want to tell them that actually the answer is the letter e, which just seemed so banal in the moment."
He added: "Before I finally revealed the 'correct' answer to the riddle, to a largely unimpressed audience, I fielded other guesses that continued along a similarly existential vein.
"There was 'NOT everything', 'all stuff', 'the end', and maybe my favourite, 'nothingthing'."
The teacher's story has since gone viral on Twitter, receiving more than 73,000 retweets.
Social media users were impressed by the answer "death", saying it was a "better answer" than the letter e.
One person commented: "See, it's things like this (as well as my son's insights) that give me a lot of hope for the future".
Another added: "Gen Z are all existential nihilists aren't they".