Surely access to contraception should be improved, no?
OP if you think 13 year olds will stop having sex you are naive! Improving access to the pill, and to condoms, doesn't encourage anybody to have sex, but it does encourage those that are going to do it to do it safely.
I had sex at 13. I was mature for my age, and fairly clued up. I took myself off to the local Brook Clinic, and got the pill and a load of condoms. I had a great relationship with my parents, had good self esteem, was happy etc. I just wanted to have sex. Shockingly, I'm 26 now and have managed to never get knocked up or catch an STI.
Ultimately, the more sex and contraception is out in the open, and not treated as a dirty secret, the more our teenagers will talk about it, the better educated they will be and the less curious.