If they are getting pregnant at 13 years old, then clearly, sex is not adult material only. You may wish for them to have carefree childhoods, but if their friends are having boyfriends and girlfriends at 5th and 6th grade, and getting pregnant by 7th or 8th grade, some education is in store.
I do hope they are talking about incriments of sex ed, like, as someone mentioned, naming body parts, and good touch/bad touch. Even with physical examinations of kids, I always have to check off the box "discussed good touch/bad touch" or some such equivalent, even for 3 and 4 and 5 year olds.
When I examine the kids, I've been taught to say, I can only examine if mom says it's okay. Mom is it okay? and mom nods her head.
Other healthcare providers say "Only doctors and nurses can look" or some such thing. As the kid gets older, we ask, do you know anyone with a boyfriend? Do your friends have boyfrinds? Do you?
And basically go from there. If they're too immature for more info, then leave it. If they are nearing 10 or 11, we say, "If and when you do have sex, even if it's way way in the future, like when you're 30, always always wear a condom. It's the safest way." At least that much is in their minds, and that's hopefully what they'll remember when the time comes.