1.You do nothing. It’s a perfectly natural thing and you feel happy for them. Advantages/Disadvantages: You are a very mature person. If you’re not, I suggest you choose one of the other options.
2."Please, Mum and Dad. Don’t have sex. I don’t want another brother or sister!" (start sobbing or pull a puppy dog face) Advantages/Disadvantages: Unlikely to stop them. Still perhaps worth a try.
3."Mum, Don’t degrade yourself!" Advantages/Disadvantages: Parents may become too embarrassed to have sex. Dad may never speak to you again.
4."Mum you can’t have sex with Dad, his penis is too small!" Advantages/Disadvantages: Mum will give you a weird look (as how would you know how your Dad’s penis length). She is also probably going to know the size anyway. As with option 3, Dad may never speak to you ever again.
5."Go for it, you two must be real demons in bed! Go Mum and Dad!" (as an added touch, you could proceed to do a cheerleader dance as well) Advantages/Disadvantages: Parents will be taken aback, may feel too uncomfortable to have sex. It’s a pretty mean thing to do embarrassing them like that. In fact if their both demons, then since you’re the offspring, you’re probably the devil, 6."I thought you guys didn’t do it anymore. When you were younger, of course, but now your parents, it’s just unnatural. God/Jesus wouldn't have wanted it." Advantages/Disadvantages: Will likely piss both Mum and Dad off (but not stop them having sex).
7."Nice one Dad! Two different women on the same day!" Advantages/Disadvantages: You’re cruel. This option can be changed around (i.e. Mum is the one having the affair). You might feel a bit guilty if they get divorced as a result (but at least they won’t be having sex if that happens).
8."Mum, Dad, this is a particularly good time to show you my report card." Advantages/Disadvantages: If very bad, may spoil the mood.
9."Mum, you whore!" Advantages/Disadvantages: Not a very nice thing to say. Mum may actually kill you for that. Choose this option only if you’re both evil and incredibly brave.
My parents divorced when I was 10, so I never had that problem.
On the other hand, I did have the problem of my dad using me to go on day trips in the hope my mum would come along for him to try and win back over. Happened all the way through to my early teens. Cringeworthy.
That's what all parents tell their children (that's what my parents tell me, but I bet their lying, lol)
Uh...why would your parents even tell you about their sex life or lack of it at all? ~~~ My father sleeps on the sofa and they'd divorce if they had any money, so.