There's a vulgar version from, I think, Oxfordshire, that I learned many years ago. It follows a very familiar pattern...

Pretty little Mary, sweeping up the room,
She untied her apron strings to make a bit of room.
In comes the master and unto her did say,
'What's trhat you've got there underneath your apron?'

'Master, Oh Master, Oh master,' then says she,
'It's nothing but a muslin gown my mother sent to me.
I had nowhere to keep it, to keep it safe from harm,
So I tucked it snugly underneath my apron.'

But then a few months later a baby boy was born,
Born without a father, without a name at all.
Back comes the master and unto her did say,
'Now I see what you had underneath your apron.

'Was it in the parlour, was it in the hall,
Was it in the drawing room or in the house at all?'
'Oh no it was in the garden, up against the wall,
That he tucked it snugly underneath my apron.'

'Was it by a tinker, or was it by a clown,
Was it by a soldier who fights for England's crown?'
'Oh no it was by a sailor, who sails the raging main,
And he tucked it snugly underneath my apron.'

So come all you fair maids, this warning take by me,
Never trust a sailor lad an inch above your knee,
For if you do you'll rue the day, he'll leave you in the lurch
Once he's tucked it snugly underneath your apron.