Oh some of these are fab!
By some kind of miracle, my DCs have never repeated a swear word in their lives, despite DH and I swearing like troopers. Well, not within earshot anyway! But I work in Early Years and I have heard some gems, let me tell you.
A 3 year old girl, on her taster day, had a sticker with her name on. One of the other girls innocently asked 'what does that say?' New girl replied 'it says fuck off'
We also had a 4 year old, the son of one of my friends, who watched me struggle to assemble a 'pop up' tent for 5 minutes then proudly said 'MiteBite, you just need to get a fucking man in'.
His mum was more horrified about the misogyny than the swearing 
And my absolute favourite, a lovely little 3 year old boy, prone to the odd bad mood in the morning aren't we all? Another member of staff saw him walk in with a face like thunder, and said 'oh Jimmy, cheer up, it's a lovely sunny day'.
He replied 'oh just fuck off Sue' which was exactly what I felt like saying to her and went to sulk in the book corner 