"I was struggling in so many areas of my life," recalls Ellie, 18, who lived in a foster placement for three years from the age of 14.

"I'd go out, get drunk, get arrested. I met this guy from youth offending, and at first he was a really nice boy. But then things started to change. I'd hold his drugs, his money, his gun. It got really abusive, mostly mental. He used to say some pretty horrible things. And even now I have some confidence issues. It was pretty damaging."

Ellie's foster mother discovered Ellie was in a sexual relationship when she found a used pregnancy test. Ellie says she was then made to go for tests to see if she'd contracted any sexually transmitted infections.

"That's when I found out I had chlamydia," she says. "This was the boy who I thought was the love of my life. It was the love I should have got from my parents."

Despite what she remembers affectionately as a "close relationship" with her foster mother, Ellie says they never sat down and talked about the implications of her being sexually active. "I felt really awkward. I lost my virginity at 14 and I didn't want to say," she explains. "It was not something that was spoken about."

It's a sensitive time for any teenager when they start to explore their sexuality. But almost by definition it's harder for young people in care. They are known to be vulnerable to sexual exploitation. For many, the sexual or physical abuse that has resulted in them being taken into care means they start from a different place when they begin to negotiate adult relationships.

Unfortunately, the question of who is looking after the sexual health and wellbeing of young people in care is difficult to answer. This is partly because the foster carers with whom they are placed do not have legal parental responsibility, and cannot keep information to themselves if they are concerned the young person may be at risk of serious harm.

"Children coming into fostering families will recognise a level of surveillance about their lives," says Diane Heath, membership support consultant at the Fostering Network. Though she says it's right that foster carers must share some disclosures, "I think that lack of confidentiality can act as an inhibitor."

It's unlikely that children will feel happy talking about their concerns if they're worried their most private thoughts will become widely known in the team responsible for their care. And though good agencies will offer training in how to handle discussions on sex education and relationships, dealing with the day-to-day reality of a teenager's burgeoning interest in sex is far more complex than just following a manual, says Alan Wood, Midlands director for the British Association for Adoption and Fostering, and also a foster carer offering placements to teenage boys.

His approach, he says, is "fairly frank".

"We say this is what the law says, this is what's allowed and not allowed. The issue is about making sure the relationship between you and the young person is as positive as it can be, so we try to offer them as much choice as we can. And that means trust is easier. It's being able to create the atmosphere within the home."

Joanna Adande, an experienced foster carer who offered placements to teenagers and now works at the Fostering Network, acknowledges that some of the conversations she's had have been "very difficult for me".

When she began fostering, Adande recalls: "I had to deal with my feelings around young people being sexually active at a very young age, and sometimes being very promiscuous. I had to learn not to use language that was interpreted as rejecting. You often have to go about things in a roundabout way as opposed to reacting from an emotional point of view. You have to be calm ... and professional."

All children's sexual wellbeing rests on their feelings of self-worth, says Kevin Williams, chief executive of the fostering and adoption charity TACT. "When children are abused and neglected, that has an impact on their self-esteem and so they are vulnerable because of their early experience. They're looking for stability, reassurance, affection.

"So yes, you need a strategy to look at their sexual health," Williams adds. "But alongside that you need a strategy to build up their self-esteem and confidence."

A young person who is looked after "may never have seen a healthy consensual relationship in practice", points out Lisa Handy, co-ordinator of the Sex Education Forum at NCB (National Children's Bureau).

And because they often move frequently, she adds, young people in care may not have had the chance to develop positive long-term relationships with friends. This gap in their experience may mean they don't have the opportunity to develop the perspective, skills and sense of security to stand up for themselves and negotiate what's reasonable and what they want from a sexual relationship.

When it comes to crunch-time and a child plucks up the courage to open a sensitive conversation, foster carers can feel very anxious about what kind of guidance they are and aren't allowed to give, says Heath.

She says that all services should have an explicit policy on sex and relationships education "and foster carers must know about their own service's policy on what they can and can't do".

Adande agrees: "Fostering service providers have to get their act together in the training they provide, and have a clear policy regarding the tension between enabling young people to make choices and protecting them. Often, we're left not knowing what the policy is and doing things from instinct, which isn't the best way."

Even though there are some professionals who will respect confidentiality – GPs and other sexual health services – it may be that some young people would prefer to have the discussion, no matter how fraught with potential embarrassment, with someone who knows them.

"I wish I'd had that conversation about the consequences with my foster mum," says Ellie. "I think it was her job to bring it up. It's going to be an awkward conversation no matter who you have it with, but we had a really close relationship and she could probably have got through to me."

Some names have been changed