My 2 year old DS says 'bugger', on purpose, as clear as day, because he's heard us say it and he obviously likes the reaction he gets when he says it. I find this hilarious and also very embarrassing, depending who is listening when he says it.
He also says, unintentionally:
'shite' ('light')
'tit' ('sit')
cock ('clock')
Anyone else's child swear like a sailor?