Here is a little tip for how I remember to have ongoing conversations about sex in our house: 

I do it every Labor Day. 
I’m firmly of the belief that the “sex talk” should be a continued developmental conversation that evolves and educates throughout childhood, but it’s easy to let years go by without making the time to broach a topic that, at least in our house, kids would rather avoid. So Labor. Day is a reminder for me to do an annual check-in with my kids around their sexuality. 
For my 7-year-old, we will do a refresher on inappropriate vs. appropriate touch, and this will be the year we explain how babies are made. For my 9-year-olds, who already know the basics, the conversation will be around puberty. For the 11-year-old, we will talk about masturbation, consent, and internet pornography. As they get older, we will go into more detail about birth control, and also reasons for delaying sexual activity. (Although, I do try to keep these lines of communication open, and we had a hilarious conversation about “sex goggles” in the car the other day, wherein I attempted to explain how getting sexually involved with someone you aren’t in love with can lead you to believe that you are more in love than you really are.) 
I try to keep our talks centered on things they are developmentally able to process, but at the same time, I try to get ahead of things, so that they understand what is happening with their bodies BEFORE it happens. I also try to get ahead of their peers: meanings when kids are alone and inevitably talk about sex, my kids aren’t hearing anything that they haven’t already heard from me. Because (hopefully) I am a better source on the topic than the information their friends have cobbled together.
 And a part of this conversation with each kid is an invitation: ASK ME ANYTHING. I give them the chance to have anything they want to know explained or defined. Wanna know what that curse word means? Heard a rumor about sex from your friends that you want explained? Have questions from our talk last year, or from something they’ve seen or heard in the media? I let my kids know that I am here to talk about anything, and that nothing they say will shock me. 
My hope is that this level of openness will continue through the teen years, when they may need a confidant as they begin dating and experimenting sexually. But Labor Day serves as my prompt to be intentional each year.