Millions of Kenyan children miss out on school because they are forced to work, are married or trafficked, the child rights charity Plan International said on Monday.
In Kenya, more than 80 percent of children attend primary school but less than half receive a secondary education, according to the United Nations children's fund, which leaves them vulnerable to exploitation.
"Child marriage, child labour and child trafficking: we have a high correlation between those three areas and children not being in school," Plan's regional director Roland Angerer told a news conference.
"There is also a reverse correlation that means if children are in school then the risk that they are exposed to one of these three threats is much lower."
Primary education is free in Kenya but fees ranging from about $100 to $1,000 lock millions of poor children out of secondary school.
In Kenya, there are around one million child labourers, aged between five and 17, according to the government. Nine out of ten live in rural areas.
"Poverty is the main driver why children are being sent to work," Angerer said.
Most boys work on farms and girls do household chores while their mothers are out at work.
"These girls, they are 10 years, 12 years old," said Angerer. "They get up at five in the morning. They fetch water. They make fires. They cook. They look after siblings at home."
By the time the girls go to school, they are too tired to concentrate or do homework and usually end up dropping out, he said.
Child labour is illegal in Kenya but the law is not enforced.
"It's a toothless law. There are hardly any penalties ever issued against people who employ children," said Angerer.
Poverty also drives child marriage in Kenya, as well as traditional cultures which seek to prevent pre-marital sex.
"Poor families expect something in return for giving their daughters away in marriage," said Angerer. "They get some bride price [dowry] for them and if they are poor this is a considerable income for the family."
In Kenya, one in four children is married by the age of 18. There are considerable regional variations, with rates as low as seven percent in the capital, Nairobi, and as high as 56 percent in the northeast of the country, Plan said.
Data on child trafficking is harder to come by.
Up to 17,500 persons are trafficked in Kenya every year and 50 percent of them are children, Plan said, citing a 2008 report by the International Organization for Migration.
"They are trafficked into the country or from rural areas to urban areas or tourist centres basically for three purposes - commercial sex work, domestic work and agricultural work," Angerer said.
"The main driver is poverty and what is really sad to see and to hear is that in many places parents themselves are colluding with child traffickers to give away their children."
Increased access to secondary education would protect some of these children, Plan said.
"The majority of children who are being trafficking have finished primary school and have nothing else to do," Angerer said.
"If we can offer a good transition from primary to secondary school, the risk of being trafficked, of being exposed to traffickers, of being lured into some dubious opportunities is much lower."
Last week, Kenya's president, Uhuru Kenyatta, promised to introduce free secondary education within three years.