We know we shouldn't laugh, (it only encourages them to do it more) but toddlers swearing is funny.
Hearing the f-word or the s-word (we're being discreet in case little eyes are around) proudly uttered by a tiny mouth is just so incongruous, it rarely fails to elicit a smirk or a guffaw from onlookers.
Whether it's in context - ie. when they've fallen over or stubbed their toe - or just an unfortunate mispronunciation of a word like "castle", the unexpectedness of a small child swearing leaves us in stitches.
We challenge you to keep a straight face while watching the Buzzfeed video above... if you can, you're a better person than us.