A BBC Africa Eye investigation has revealed how women, known as “madams”, have involved children as young as 13 in prostitution in Kenya.

In the transit town of Maai Mahiu, in Kenya’s Rift Valley, trucks and lorries pound the streets day and night transporting goods and people across the country into Uganda, Rwanda, South Sudan, and the Democratic Republic of Congo.

The key transport hub, just 50km (31 miles) east of the capital, Nairobi, is known for prostitution, but it is also a breeding ground for child sexual abuse.

Two undercover investigators, posing as sex workers wanting to learn how to become madams, spent months earlier this year infiltrating the sex trade in the town.

Their secret filming reveals two different women who say they know it is illegal and then introduce the investigators to underage girls in the sex industry.

The BBC gave all its evidence to the Kenyan police in March. The BBC believes the madams have moved location since then. The police said the women and young girls we filmed could not be traced. To date there have been no arrests.

Convictions are rare in Kenya. For successful prosecutions, police need testimonies from children. Often vulnerable minors are too afraid to testify.

The BBC’s grainy footage filmed on the street in the dark showed one woman, who calls herself Nyambura, laughing as she says: “They’re still children, so it’s easy to manipulate them by just handing them sweets.”

“Prostitution is a cash crop in Maai Mahiu; the truckers basically fuel it. And that’s how we benefit. It’s been normalised in Maai Mahiu,” she explained, adding that she had one girl as young as 13, who had already been “working” for six months.

“It becomes very risky when you’re dealing with minors. You can’t just bring them out openly in town. I only sneak them out at night in great secrecy,” Nyambura said.

The act of prostitution by a consenting adult is not explicitly criminalised under Kenyan national law but it is banned by many municipal by-laws. It is not banned in Maai Mahiu, which is part of Nakuru county.

Under the penal code it is illegal to live from the earnings of prostitution, either as a sex worker or third party facilitating or profiting from prostitution.

The trafficking or sale of minors under the age of 18 carries a prison sentence ranging from 10 years to life.

When asked whether the clients wear condoms, Nyambura said she usually made sure they had protection but the odd one did not.

“Some children want to earn more [so don’t use them]. Some are forced [not to use them],” she said.

In another meeting, she led the undercover investigator to a house where three young girls sat huddled on a sofa, another on a hard-backed chair.

Nyambura then left the room, giving the investigator an opportunity to speak to the girls alone.

They described being repeatedly abused for sex, on a daily basis.

“Sometimes you have sex with multiple people. The clients force you to do unimaginable things,” said one of the girls.

There are no recent statistics on the number of children forced to work in Kenya’s sex industry. In 2012, the US State Department Country Report on Human Rights Practices in Kenya cited an estimate of 30,000, a figure derived from the Kenyan government and now defunct non-governmental organisation (NGO), Eradicate Child Prostitution in Kenya.

Other studies have focused on specific areas, especially along the country’s coast – known for its tourist resorts. A 2022 report for the NGO Global Fund to End Modern Slavery found almost 2,500 children were forced into sex work in Kilifi and Kwale counties.

A second undercover investigator gained the trust of a woman who called herself Cheptoo and had multiple meetings with her.

She said selling young girls meant she could “earn a living and be comfortable”.

“You carry out this kind of business in great secrecy because it is illegal,” she said.

“If anyone says they want a young girl, I ask them to pay me. We also have our regulars who always come back for them.”

Cheptoo took the undercover investigator to a club to meet four of her girls. The youngest said she was 13 years old. The others said they were 15.

She opened up about the profit she makes from them, saying for every 3,000 Kenyan shillings ($23; £17) the girls deliver, her share was 2,500 shillings ($19; £14).

At another meeting, in a house in Maai Mahiu, Cheptoo left the undercover investigator alone with two underage girls.

One of them told her she had, on average, sex with five men a day.

When asked what happened if she refused to have sex without a condom, she said she had no choice.

“I have to [have sex without a condom]. I will be chased away, and I have nowhere to run to. I am an orphan.”

People outside the UK can watch here

Kenya’s sex industry is a complex, murky world where both men and women are involved in facilitating child prostitution.

It is not known how many children are forced into sex work in Maai Mahiu, but in this small town of around 50,000 people it is easy to find them.

A former sex worker, known as “Baby Girl”, now provides refuge in Maai Mahiu for girls who have escaped sexual abuse.

The 61-year-old worked in the sex industry for 40 years – first finding herself on the streets in her early twenties. She was pregnant and had her three young children with her after fleeing her husband because of domestic violence.

At her wooden kitchen table in a bright parlour at the front of her house, she introduced the BBC to four young women who were all forced into sex work by madams in Maai Mahiu when they were children.

Each girl shared similar stories of broken families or abuse at home – they came to Maai Mahiu to escape, only to be violently abused again.

Michelle described how, at 12 years old, she lost her parents to HIV and was evicted on to the streets where she met a man who gave her somewhere to live and began sexually abusing her.

“I literally had to pay him in kind for educating me. I reached my limit, but I had no-one,” she said.

Two years later, she was approached by a woman who turned out to be a madam in Maai Mahiu and forced her into sex work.

Lilian, who is now 19, also lost her parents at a very young age. She was left with an uncle who filmed her in the shower and sold the images to his friends. The voyeurism soon turned into rape.

“That was my worst day. I was 12 then.”

When she escaped, she was raped again by a truck driver who took her to Maai Mahiu. It was here, like Michelle, where she was approached by a woman who forced her into sex work.

These young women’s short lives have been fuelled by violence, neglect and abuse.

Now, housed by Baby Girl, they are learning new skills – two in a photography studio and two in a beauty salon.

They also assist Baby Girl with her outreach work in the community.

Nakuru county has one of the highest rates of HIV infection in Kenya, and Baby Girl, supported by US aid agency USAID, is on a mission to educate people about the risks of unprotected sex.

She has an office at Karagita Community Health Centre, near Lake Naivasha, where she works providing condoms and advice.

However, with US President Donald Trump’s decision to pull USAID funding, her outreach programmes are about to stop.

“From September we will be unemployed,” she told the BBC World Service, adding how worried she was about the young women and girls who depend on her.

“You see how vulnerable these children are. How would they survive on their own? They are still healing.”

The US government did not respond to comments in this investigation about the likely impact of its funding cuts. USAID officially closed last month.

For now, Lilian is focused on learning photography and recovering from abuse.

“I am not afraid any more, because Baby Girl is there for me,” she said. “She is helping us bury the past.”