Since the start of the Russian war of aggression in Ukraine, almost two-thirds of all Ukrainian children have had to leave their homes, according to the UN children's fund Unicef.

Of the approximately 7.5 million children under the age of 18, 2.8 million have been displaced within the country and two million have fled abroad, said the head of UNICEF's emergency aid programs, Manuel Fontaine, on Monday in New York.

According to UNICEF, at least 142 children have been killed in Ukraine in the seven weeks since the Russian invasion.

In reality, however, the numbers are likely to be significantly higher, the organization said.

The judiciary in Ukraine itself said on Tuesday that at least 186 children and young people had been killed and 344 injured.

"The war continues to be a nightmare for the children of Ukraine," Fontaine said.

UNICEF: Never before has there been such a large number of refugee children in such a short time

More than 4.5 million people have fled abroad since the beginning of the Russian war of aggression on February 24, it said - around 90 percent of them are women and children.

Around seven million more were also displaced within Ukraine.

"In six weeks, it's just incredible," said Fontaine, who says he has never seen such a large number of refugee children in such a short time.

Of the Ukrainian children who have not yet fled, almost half are at risk of starvation, Fontaine warned after returning from a visit to Ukraine.

The situation is worst in cities like Mariupol and Kherson, "where children and their families have been living for weeks without running water and sanitation, regular food supplies and medical care," Fontaine said.

The situation of children and women in Ukraine was also the focus of a meeting of the UN Security Council on Monday.

Before the meeting, the Norwegian ambassador to the UN, Mona Juul, complained that the vast majority of Ukrainian children can no longer go to school.

5.7 million children are affected by the nationwide school closures, Juul told journalists.

“We are hearing more and more about rape and sexual violence”

"Schools are important, not only for education, but also to protect children from violence, sexual abuse and even human trafficking," said the Norwegian.

Meanwhile, the UN women's organization called for an independent investigation into sexual violence in the Ukraine war.

"We are hearing more and more about rape and sexual violence," said UN Women Director Sima Bahous.

These reports would need to be independently investigated to ensure justice and hold those responsible accountable.