The UN's children's agency called Monday for Yemen to improve safeguards for kids as it discusses how to draft a new constitution, by for instance ensuring access to clean water and battling child marriages.

Yemen is currently engaged in a national dialogue as part of a UN-brokered deal that eased former strongman Ali Abdullah Saleh from power last year after an 11-month uprising against his 33-year rule.

The talks, which aim to pave the way for elections in 2014 and for the creation of a new constitution, "give us a once in a lifetime opportunity ... to ensure that the rights of children are fully baked into the constitution," UNICEF's Yemen representative Julien Harneis told reporters in Geneva.

A major problem in Yemen, ravaged by years of factional strife and widespread poverty, is that there is no clear definition of what constitutes a child, making it difficult to battle child marriages, or to ensure that juvenile offenders are not tried -- and executed -- as adults, he said.

"Depending upon which bit of legislation (you look at), a child in Yemen can be somebody under 14, somebody under 15, somebody under 16 or somebody under 18," Harneis pointed out.

This, on top of the fact that only around 21 percent of births are registered in Yemen, meaning many people do not know their exact age, and that there are no laws against child marriage, means the practice is widespread, he said.

"We see children who are married at the age of 9 or 10 years old," he lamented.

Yemen does have laws against executing people who commit crimes as children, but, Harneis said, the laws are "insufficiently clear and there are difficulties in proving people's age at the time of offence."

As a result, there are currently 25 juvenile offenders on Yemen's death row.

The lack of clarity around what constitutes a child and how old most people are has also contributed to making Yemen fertile ground for human trafficking of kids, especially boys, according to UNICEF.

From June 2012 to May 2013, 788 rescued children who had been trafficked were received at a UNICEF-supported care centre in Haradh, in central Yemen.

"Given that these figures only include children that have been rescued, they potentially represent just the tip of the iceberg," the UN agency said.

In Yemen -- one of the world's most water-stressed countries -- there is also a desperate need to legislate how water is distributed, Harneis said, pointing out that lacking access to clean water has especially devastating implications for children.

Today, only about six percent of Yemen's water goes to households, with Yemenis on average having access to just 15 litres a day, instead of the 40 litres they should have, according to national standards.