There's a book various people have recommended on here called "Mummy Laid an Egg" - Babette Cole I think. I think it's too graphic for a 2 - 3 year old though. In fact, even for my 7 year old I decided against it - it was the "positions" page that put me off! It's a funny book but more information that I wanted!
We have an Usbourne body parts books - last section is on babies - how they are made and how they grow etc. Would be good from approx your DD's age and my 7 year old reads it herself now.
At similar age of your DD, we focused more on how the baby grows in the tummy - starts as a tiny egg and grows into a baby. I told DD baby comes out of special hole called a vagina or birth canal or sometimes is cut out (she was ecs so seen scar etc.) Also said, you needed a grown up Mummy and a Daddy for the egg to grow. (because I thought she might worry it was going to happen to her.) Later, we introduced the fact that sperm and egg meet.
Interestingly, my friend with older kids says that even at 8 or 9 years old when it's introduced at school, they don't focus much on the mechanics of how the sperm gets in!!!
IMO, think it's good to give info bit by bit so that you are giving the right amount at the right time. Recently DD who was about 6 at the time asked me "How are we made?" I was about to launch into a full explanation when she qualified the question and it turned out she was really asking about blood, veins, bones etc!! So, I now check on the question!