So my DCs have started asking based on friends/family members being pregnant. They are 7 and 4. Is it too young to start talking to them using the proper words? I've bought a book but it uses the full terms for body parts and shows a couple in bed cuddling and the words 'sex' etc. Are they going to be running around suggesting that couples cuddling are having sex? 
Probably overthinking this but as a single parent it's left to me and I don't want to make a mess of it. Should I ask their teachers first? Any advice appreciated!