I was 12 when I first got to know some sexually active teens (at Girl Scout camp!) and that really got me thinking about what kind of experiences I wanted for myself and when. The fact that these slightly older girls were enjoying sex, and that they hadn't suffered a lot of social disapproval for it, was heartening to me. I was concerned tho that they seemed to think contraception reduced their risk of pregnancy and disease to zero, which I knew wasn't true. I also got the impression that one of the two girls was kind of using the guys, and sex, to feel "wild" and grown-up, and that it didn't really mean as much to her as I thought it should. I'd always thought of sex as something in my distant adult future; now I was realizing that the future was drawing closer and that within just a few years I would need to be prepared to make decisions about sex. (I didn't see it as inevitable that I WOULD have sex as a teenager, just that the opportunity would be there.) What would I do differently from those girls?
I think most young teens or preteens have an experience kind of like that: realizing that people their own age or a little older are having sex. The trick for parents is figuring out when that has happened and figuring out how to talk about it in a way that supports their kid's ability to make responsible decisions, instead of lecturing about how sex will ruin the kid's life. (Personal beliefs should be conveyed, of course, but with a tone of, "These are some important ideas to consider" rather than, "This is what you'd better do or else!!!") I guess my suggestions are to listen for anything the kid says about sex, to look for naturally occurring discussion starters (kid is reading a teen novel involving sex, you see a news article on "virginity pledges," you're working on a pro-choice or pro-life cause, etc.), and to remember that slumber parties and camp and similar events where teens spend the night together tend to be a forum for talk about sex.
After a couple of years of mulling it over, reading everything I could find on the subject, and discussing with some experienced relatives and friends, I decided that before I had any kind of sexual activity with another person, I should:
*like him--not just feel attracted to him, but really like him as a human being and be able to have a good conversation
*trust him not to laugh at me, hurt me on purpose, or treat me disrespectfully afterward
*feel comfortable with him seeing me naked
*be familiar with my own body and orgasmic response
*be confident about setting limits on how far we were going
*be prepared to learn what guys like instead of getting overwhelmed by uncertainty
and before I had intercourse, I should also:
*feel comfortable insisting that he provide and use condoms
*know what kind of contraception in addition to condoms (which are only 85% effective!) I would use and where I would get it
*have a plan for what to do if I got pregnant
*be able to talk with him about and agree on all of the above
*feel ready to accept whatever pain might be involved in losing my hymen, and feel that he would be sensitive about that.
There may have been a few more things on those lists, but those are the ones I can think of now. Notice there's no mention of romance or monogamy--those weren't important things to me then, and while I've since learned how wonderful it feels to be in love, I still don't think that's a mandatory prerequisite for sex...and I've never figured out what people think is so great about monogamy!
Actually, I think that for adults as well as teens, the ideal way to start a sexual relationship is with a solid friendship, not a dating relationship. (What I mean by "dating relationship" is the kind of thing where you barely know each other until one of you asks the other out, and then you share planned activities whose focus is on "romantic" behavior and entertainment--that's not a way to get to know each other on the kind of genuine, intimate level that makes for healthy sex.) Being friends motivates you to behave kindly in relation to sex and to either maintain the relationship or end it well, because if you're unkind or end it badly, you lose a friend. When you don't have that at stake, it's easier to cast someone aside for some trivial flaw and never see each other again and move on to other fish in the sea. So, maybe one of the best ways to help your child have healthy sexual relationships is to encourage friendships with both sexes!