Its not a vagina.
Your three year old likely isn't engaging in sexual activity, or shouldn't be.
So why would they be using their vagina?
Go read an anatomy book, and come back and tell us what word you're going to make your child shout in future.
Can't see us using tuppence though just sounds weird.And at last...it only took 5 pages.!bluetonic! said:It's not though is it! The vagina is the internal canal leading up from the vulva.. The vulva being the external structure which is broken down into several parts.

monkey knuckle.
twinkle in our household
If you go with "Tuppence" you might have some confusing situations when people start saying things like "I'll just throw in my 2p".
What's wrong with using the actual word "vagina"? Why teach your child that their own body is taboo and to be referred to only in nervous euphemisms? She'll be subject to enough insecurity later on anyway.

There used be a victorian novel on my grandma's bookshelf, it was called "Fanny by Gaslight". The thought of it boggled my 9-year self's mind. It was perfectly innocent, of course.

interesting topic - have just consulted with my daughter (18) - when she was little, she herself called it her "front bum" becuase it was at the front - nowadays, she is well aware of the incorrect term, vagina, and every other name known to man, that lady bits get called.
she says the word "vagina" and "vag" - sound unhospitable and gungy, not somewhere you'd want to go - she also loathes the words pussy, minge and clunge. I asked her what she was comfortable with calling said part, she replied "front bum" lol
*my granny called it a ha'penny - her advice was always "keep your hand on yer ha'penny" - I just took that as cover it, and don't let anythin in there and you'll be fine
just go with whatever you're comfortable with.