Ha! i am laughing as I am amazed it has taken her this long to discover the differences! My husband became very uncomfortable when DD was 2 and stared at his bits wanting to know what they were!!! Dood I am sure is that little cherubs interpretation of doodle! I had to do the talk about girl bits and boy bits...nothing more in depth apart from the difference in anatomy! I had to do it so dad could continue having a bath with DD without major scrutiny! Once it was explained to her she was happy! After a week or so of being informed that this animal was a boy and thatoone was a girl because of the different bits, her curiosity was satisfied. I am sure that's all it is curiosity...the sooner you address it, the sooner it will fade into insignificance. If you make it a no go subject...she will continue to ask the questions!

LOL! THAT'S SOOO CUTE! MY DAUGHTER GOT THE LOVELY WORD DICK FROM HER OLDER BRO!!!!!

DON'T STRESS EVERY CHILD GOES THROUGH THIS ENTIRE PHASE OF BEING COMPLETLY ENTHRALLED WITH THE OPPOSITE BIT'S & PIECES!

JUST TELL HER THE TRUTH! LET HER JUST KNOW THAT BOY'S HAVE PENISES & GIRLS HAVE VAGINA'S! (I THINK DOOD IS A REALLY CUTE TERM TO USE ESPECIALLY AT 4!)

HANG IN THERE! SHE SOUNDS ADORABLE!

 You have been given some excellent advice here and from Dad hehe! You have one very clever daughter there ( 4 going on 14) and you need to be  honest with her both of you. And don't tell her it is rude or she will think it is something bad, it is completely natural for kiddies to ask questions about things they don't understand, it is the only way they learn, if she doesn't get the answers from you she will then ask other people.

ABC Books have a great collection of books on a whole of subjects that help parents approach certain subjects with their children, maybe worth looking into if your so uncomfortable in telling her.

I wish you well sweetie, be honest with her.

Yep have to agree with soozntone

Don't make a big deal of it because kids have a sense for things that sound like no go zones it only makes them more curious.

Be matter of fact ! Use the same tone that you would when explaining anything else she might ask.

Perhaps try " it's not a dood it's a penis and boys have a penis, girls have a vagina, so you and mummy have a vagina and daddy has a penis" .

kepp it simple and honest ! Kids sem to have a radar for parents trying to avoid a topic. Of course you don't have to go into great detail at 4 , but neither should you try avoiding it either.

Perhaps use the discussion to say to her your vagina is a private part and we don't talk about it outside the house. But you can come and tell mummy and daddy if anyone touches your vagina because mummy and daddy would like to know if that happens.

it's not too early to give her the tools to help keep her safe !

I've been thinking about this question for a bit.  I imagine that your daughter has picked up on the idea that this is an uncomfortable topic, and that's why she's doing it.  I have two boys - a four year old and a three year old, who have noticed the difference between themselves and their sisters.  They sometimes will tell me in a matter-of-fact way what their sisters don't have. 

At three, my son doesn't really get the idea of manners (he's starting to do polite things as told, but doesn't understand why), but at four, my older son does, and can be taught what is good manners and what isn't.  If you tell your daughter that it's not manners to talk about those things to other people, because they might be uncomfortable, she might understand.  I'd not make it a taboo topic at home, but help her to see the difference in at home talk and out/visiting talk.  Also, don't get flustered or upset when she does ask about it, because that will make it a game for her.  Keep it matter-of-fact, short and sweet, only answer what she asks and don't elaborate, or you may give her more ammunition.  The rest of that conversation can be had as she grows and when you decide she's ready for it.

I'm assuming your daughter has seen both you and your partner naked..  Just explain to her matter of factly the difference between men and women.  ie.  Penis, Vagina, Breasts.  You don't need to tell her what men and women do with the different parts.  Though you could explain that breasts are for feeding.

If she asks if you have a "dood" then just say No, mummy is a girl..  Girls don't have "doods".  If she asks you partner just have him reply.  Yes, Daddy is a boy, Daddy has a "dood".  If you can it is probably better to teach her the correct words too..  Penis and Vagina.

Just remain calm and always answer the same.  If you seem flustered she will continue for longer because she will be able to sense your discomfort.  (not to be mean, she may not realise it's discomfort).