In a report marking the 30th anniversary of the UN Convention on the Rights of the Child, UNICEF said poverty and marginalization continued to put the well-being of millions of young people at risk.

UNICEF chief Henrietta Fore said in a statement that in addition to "the persistent challenges of health, nutrition and education, children today have to contend with new threats like climate change, online abuse and cyberbullying."

What's Changed Since 1989?

According to the report, the global mortality rate for children under five has fallen by about 60% over the past 30 years.

More children today also have access to primary education — the proportion of kids who don't attend school has dropped from 18% to 8%. But the report warned that progress has stagnated, with little change since 2007.

"There have been impressive gains for children over the past three decades, as more and more are living longer, better and healthier lives. However, the odds continue to be stacked against the poorest and most vulnerable," Fore said.

Under-fives from the poorest households are twice as likely to die from preventable causes than children from the richest households, the report said.

Although more children are immunized than ever before, vaccination rates have slowed over the past decade, contributing to a resurgence of diseases in some countries. Only half of poor children in sub-Saharan Africa are vaccinated against measles, for example.

Some girls are now more at risk of a child marriage than they would have been in 1989.

The report also stressed that children are most at risk of the impacts of climate change, such as extreme weather and food and water insecurity.

'We Must Act Now'

Fore called for these challenges to be tackled through "innovation, new technologies, political will and increased resources."

"We must act now — boldly and creatively," she said.

The Convention on the Rights of the Child was adopted by the UN General Assembly on Nov. 20, 1989. The treaty has been ratified by all UN member states bar the U.S.