The scouting movement celebrated its 100th anniversary last year
The Scout Association is to start offering its members sexual health and relationships advice.
New guidance, geared mainly to 14 to 18-year-olds, advises leaders to discuss contraception and encourage resisting of peer pressure to have sex.
Scout groups can also organise trips to sexual health clinics and give details of other helpful agencies.
The move follows requests from leaders for association guidance on how to deal with members seeking advice about sex.
Chief Scout Peter Duncan said: "We must be realistic and accept that around a third of young people are sexually active before 16."
The guidance says leaders should "encourage young people to resist pressure to have early sex" and to talk to their parents or carers, but "should be prepared to offer appropriate information" if it is needed.
The Scouting Association said some young people might feel more comfortable discussing sexual issues in the informal setting of a scouts group.
The greater focus will be on the explorer scouts, aged 14 to 18, but leaders of scouts aged 10 to 14 are told youngsters may seek advice and should be given information and suitable local contacts.
Leaders of beavers and cubs - ages six to 10 - are told it is unlikely they will need to take "positive action".
It is so much more meaningful to discuss these issues with people of our own age and in a context we know we can trust
Suggested activities for older scout groups include discussions about different religious beliefs regarding sex, and "how to say no" role-plays.
The new guidance says scout leaders can even give out condoms but "only if they believe the young person is very likely to begin or continue having intercourse with or without contraception".
Contraception can only be offered if without it "their physical or mental health are likely to suffer".
A visit to, or by, a sexual health clinic may help to "break illusions of what these services are and improve the uptake of advice".
Mr Duncan said: "I firmly believe that the confidence, skills and self-esteem young people gain through the incredible range of activities scouting offers is the best way to equip them not to feel pressured into a sexual relationship before they are ready."
Explorer scout Amy Brunsdon, 17, said: "Many young people are already sexually active, and it is great news the Scout Association is providing this new advice.
"We do get some information at college, but too often it focuses on the biology, not issues like emotional pressure.
"It is so much more meaningful to discuss these issues with people of our own age and in a context we know we can trust."
Minister for Young People Beverley Hughes also welcomed the new guidance.
"This guidance underlines the consensus among young people, parents and professionals on the importance of providing accurate information and advice on sex and relationships.