(CNN) -- Every day, 12-year-old Abed El-Elah and his 10-year-old brother leave school at one in the afternoon and head to work -- selling balloons in the park.
They work until sunset, earning 1,000 Yemeni Rials (about $4.60) a day between them. The money is never enough.
Abed El-Elah, who asked CNN not to use his surname, is one of Yemen's many child workers.
His mother died six years ago and his father, who is sick and rarely able to leave the house, has since remarried. Abel El-Elah says his stepmother encourages him and his brother to go out to work.
"I started work when I was 10 years old," Abed El-Elah said. "I have to work because my father is sick at home and I need to provide money for my family.
"I got into fights on the streets with older boys who wanted to take my money."
Yemen has a young and rapidly growing population, and there is widespread poverty. Many parents do not earn enough to support their families, so they send their children to work.
Yemen's Shawthab Foundation for Childhood and Development is one organization helping working children, among them Abed El-Elah and his brother, by providing them with food, clothes, school bags and protection, on the condition they stay at school.
But after school Abed El-Elah still goes to work. "Shawthab Foundation provides us with food and clothes but I still need to work for money," he said.
Maryam Al Shawafi, manager of Shawthab, says the organization doesn't want children to work, but it can't force them to stop.
It's the problem at the heart of child labor in Yemen -- simple economics.
Roberta Contin is project director for Access-Plus, part of development organization CHF International, which combats exploitative child labor in Yemen.
Contin says child labor is a growing problem in Yemen, and the economic crisis has made it worse.
Most children have to work to support their families, while the poorest families simply cannot afford school fees or uniforms, so they send their children to work instead, according to Contin.
In Yemen's cities, children often work in restaurants, peddling goods on the streets, or collecting garbage for recycling. It's not uncommon to see boys working as car mechanics or in metal workshops, surrounded by dangerous equipment, said Contin.
In rural areas children usually work in agriculture. Many are involved in the cultivation of qat -- a natural narcotic that's legal in Yemen -- often working alone at night to guard qat plants from thieves, she added.
It's dangerous work for children. Some are exposed to hazardous chemicals and others complain of being beaten by employers or co-workers.
Most vulnerable of all are the children who work smuggling goods -- including qat -- into Saudi Arabia. These youngsters often have to travel long distances on foot and are susceptible to physical and sexual abuse, according to Contin.
There are no definitive numbers but a 2006 cluster survey by the Ministry of Public Health and Population found that 22% of Yemeni children were involved in some form of child labor.
Results of a comprehensive 2009 survey into the scale of the problem by the International Labor Organisation in conjunction with the Yemeni government are due to be published later this year.
While Yemeni law prohibits children under the age of 14 from working, it makes exceptions for children working in family businesses, said George Abu-Al-Zulof, a UNICEF child protection specialist in Yemen.
He says a lack of monitoring means it is common for businesses to flout the law by employing young children.
"There should be inspections for the workplace, but there's not enough, which results in children as young as seven or eight being employed in hazardous work," he said.
The Access-Plus program will run until September 2011 and Contin says by then it will have helped withdraw 4,100 children from child labor and prevented another 3,000 from engaging in child labor.
Fouad Ali Naziri is one of the children it has helped. Naziri, 13, has seven brothers and three sisters, but only three of his brothers are in school.
He spent last year working unpaid with his father in construction, loading stones and sand from dawn to dusk. He has scars on this shins from where rocks rolled onto him.
After meeting Naziri and his father, an Access community outreach volunteer got Naziri re-enrolled in school. Naziri now receives remedial education to help him catch up on missed classes and hopes to one day become a doctor or a teacher.
As well as taking children out of work, Contin says it's vital to change attitudes to child labor. To that end it has run awareness programs, including training Imams to incorporate child labor issues in their religious services.
But often it's parents' attitudes that must change.
"That's the big challenge," said Contin. "It's really a matter of convincing parents and children of the benefits of going back to school or attending a vocational training course, because in the long term it will provide them with a better life."
Aroub Abdelhaq contributed to this story.