The shy topic- sex

I recently overheard my partner telling the children that their elder cousin has a baby and was shocked by the reply my 6 year old asked, "who gave her the pregnancy?' . My partner did not respond and changed the topic, i did not intervene but i knew that its time to have that shy topic.
Today's children are very bright, i remember that at the age of 10/11, i didn't know where children come from. In fact, my mother would tell us that she bought each of us from different markets. I learnt about conception while in grade 6 and that was through the science teacher and even then, i couldn't imagine that my good parents could do such a thing. But that was many years ago, fast-forward to 2018, am thinking how to talk to my children on the sex topic. I know i always talk about it, like dont let anyone touch your private parts except for mum, dont take gifts from men because they can steal children, dont go to the neighbours houses, etc. I admit children today watch alot of TVs unlike years back, they even watch adult programs in our absence and at time within. Some parts of programs i have watched with children and they would bring that part that makes you close your eyes hoping your children dont see it , but they do,....hard to tell them to go away so that you can watch your favourite program. So, all in all, they know alot and their questions are just but to validate what they know from the parent.
So, how do we approach this topic? Start from what they know, ask them what their teachers taught them, what they talk with other children and hear everything they know. It will become more interactive and will avoid alot of agony moments.
Never lie to your child, it will be unforgivable for them to learn truth from outside sources. Let the truth be saidd however agonising it be. Again, children know most of things because their is alot of media on the information and they share this information with their peers.
to be continued.............