Tell kids the honest truth whenever they ask- me 10 year old daughter asked me if it hurts “the first time you do it”- after telling her I never felt a thing, had a good sit down chat with her about everything from A-Z, soon had the other 2 in the room n it became a family discussion.
Bit worried when the missus asked “whats an orgasm” though
Kids seem to know earlier and earlier about the physical side of sex (what you stick where) – helps if you explain the emotional side to them so they understand whats involved.