I've worked in the sexual and reproductive health and rights sector for more years than I care to mention. It's a sector whose interests I am deeply passionate about promoting, but it is one that often causes me immense frustration.

I feel particularly frustrated today on the Day of the Girl. It is commendable that we should have a "day of the girl"; it is essential that we get the world to sit up and take notice of how girls are neglected, marginalised, abused and discriminated against. It is crucial that we make it absolutely and utterly clear once and for all that forced sex of any sort, at any time, under any circumstances, is unacceptable. It is critical for us to focus on ending child marriage because it violates millions of girls' rights, disrupts their education, jeopardises their health, and denies them their childhood.

And yet … something obvious is missing in all our sincere and potentially effective efforts towards ending child marriage. This month the UK all-party parliamentary group on population, development and reproductive health produced A Childhood Lost - A Report on Child Marriage in the UK and the Developing World; if you haven't time to read its 50 pages, here is the gist of the recommendations:

Enforce international conventions on the rights of the child/prevention of violence/minimum age; improve, implement and reform laws on divorce, inheritance and property ownership to give women equal rights; improve registration of births and marriages; scale up high quality education and ensure girls get equal access and hence equal opportunity; invest in programmes to make communities aware of the risks of child marriage and to effect attitudinal and behavioural change; fund shelters for women and girls affected by child marriage; invest in rolling out and scaling up programmes to prevent child marriage and support those at risk or already affected; fund research on the scale of child marriage and its consequences.

These are all sound, essential, well-considered recommendations. They focus on legal, administrative and infrastructure change as a means to achieve the goal of ending child marriage. In particular, what is pivotal to all these recommendations is establishing an internationally agreed marriageable age. These are critical steps to fixing a framework for moving forward.

This is absolutely fine. I have no cavil with it whatsoever. But – and here we come to the obvious omission – we have an unaddressed issue which is that of the age of consent: the age when you are legally allowed to have sex. As countries begin to amend the marriageable age, many amend the age of consent so the two align, if that is not already the case. Sex is regarded as something that can only start to happen when a marriage certificate is in place. This has two consequences: those who have sex before marriage are stigmatised, criminalised and rejected. And since sex before marriage is not supposed to happen, those who have sex before marriage often have no access to sexual health services because of laws, the attitudes of service providers, or because they are too afraid to go there.

You end up in the ridiculous situation in which a married girl of 16 can access contraceptive advice and services, while an unmarried 18-year-old is barred from doing so.

This is completely nonsensical, and ignores some of the most fundamental and obvious facts about sex and young people. Young people are curious. They are curious about sex. And they'll do it regardless of any social and religious strictures: young people will always find a way round any impediments of that sort, if they truly want something. This is something the sexual and reproductive health and rights community needs to dare to discuss properly and directly, and soon. Unless we genuinely, sincerely and openly accept and understand that young people want to have sex and do have sex, then setting a globally agreed legal age of marriage at 18 is only dealing with half the issue.

The question of age of consent has to be built into any recommendations aimed at banishing the abuses of early marriage. Some people will probably see it as off-topic but it should be right at the heart of any programme or policy which has anything to do with changing attitudes and actions which are damaging to young people's sexual wellbeing, not to mention their economic, educational and social welfare. Which is what early or forced marriage is.

And as an integral component in that, we must account for comprehensive sexuality education. Without education young people aren't aware of their rights, and if they aren't aware of their rights, they aren't aware of how established custom, tradition and law may infringe those rights. Without education, they are unaware of the proper respect due to them as individuals.

Critically, while it's Day of the Girl, if we want to promote an agenda of respect and rights which will bring an end to child marriage, possibly the people we need to focus on just as much as young girls … are young boys. Ironic.

Doortje Braeken is IPPF's senior adviser on adolescents and young people, responsible for co-ordinating programmes in 26 countries