The struggle of keeping a straight face
My 6yo asked me very seriously if penguins have knees. I had to excuse myself to the kitchen so he wouldn't see me losing it. He was genuinely concerned about penguin mobility. Came back and explained that yes, penguins have knees, they're just hidden under their feathers. He seemed satisfied with this answer.
These are the moments you gotta treasure. My 5yo asked me why the sky is blue yesterday and I had to really focus on not laughing at how serious he was about it.