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.
