The first thing that I will say is that it just doesn’t have to be that hard. We act like this is a major difficulty, something extremely hard to do. Embarrassing even.
To quote one of my favorite teachers… “WIMP!!!” 
She taught me during my design classes, and every time we’d do something only half-way, she’d call us wimps. The point stuck… If you’re going to do something, DO IT! Give your all, make it intentional, and be bold.
Look… The point is simple. If you don’t talk to your kids about sex and its role in the Plan of Salvation, they’re going to hear partial truths from other sources. Would you really hand off one of the most critical conversations to complete strangers, especially ones who may not have our understanding?
And you’d be surprised what kids get.
Watch that video. All 7:25 of it. They get it.
I so agree. It really isn’t all that embarrassing either, once you really kind of get past the first akwardness of naming body parts. The only time it comes back to bite you is when you hear your child describing the process/using anatomically correct terms to strangers at the park…people in the ward…relatives and friends who come to visit
And by the way, that video is a keeper.
Kids when small have their sexuality dormant… for a small kid his/her sexual organs are just like his/her nose and fingers. That would be the most appropriate age to explain the differences of sexes and the process of procreation… objectively. You should explain it without any inhibition or shame, the same way you would explain the process of ears, nose, lungs etc. Considering the social taboos, may be we should give him/her a little advice to talk about it only to you. Kids should be encouraged to to talk about it to you and even ask questions. When questions are asked, you should give them honest, objective answers.