Books. My child, when she had just turned 5, stumbled across a baby development book that also had a few pages on sex and body development in it. It was geared towards younger kids, her age, and I allowed it. It made things simple and not weird. Since then we have gotten a body safety book and another more in depth sex ed book as part of our home library. I find it handy to have books laying around. Sure, I suppose you could look videos up on youtube but I prefer the book and discuss method better. A quick amazon search on the subject will net you a bunch of books to consider and from there you can even see if the library near you has them to check out. Good luck.