When DS was 4, we told him what Mr Hope'ful version.
When he asked again at 5, we let him watch Discovery Channel programs on childbirth. He asked if its how he came and if its painful, etc, we showed him his birth pcitures. No video, as he was delivered in KKH and they dont allow it.
He is now 6 and asked in details few months ago, we googled online and show him about conception of animals, becos he loves them and has good knowledge of them. He asked why the male has to mount the female and we answer thats how life begins. He seems to understand somewhat and asked no further.
When he gets older and asked about humans, we will again google and explain in scientific terms.
We had long ago decided that whenever the question pops up, we will answer it most truthfully. It really depends on how old your child is and how much you want to tell.
Have your kid(s) asked about sanitary napkins yet? Try explaining that.... we had to do that just a few months ago...