An estimated 2.3 million people have fled Ukraine as of Thursday, including 1 million children, according to UNICEF.

Most have fled to neighboring countries Poland, Hungary, Slovakia, Moldova and Romania. Nearly 1.5 million Ukrainian refugees have fled to Poland, the U.N. High Commissioner for Refugees reported Thursday, March 10, Fox News reports.

"The number of children on the move is staggering, an indication of how desperate the situation for children and families in Ukraine has become," said Afshan Khan, UNICEF regional director for Europe and Central Asia. "Children are leaving everything they know behind in search of safety. This is heartbreaking."

Ukrainian President Volodymyr Zelenskyy and Ukraine's Ministry of Foreign Affairs said Thursday that Russian military forces shelled a children's hospital and maternity ward, which Russian officials denied.

Zelenskyy said the airstrike on the hospital left three people dead, including a child, and more than a dozen injured.

The Office of the U.N. High Commissioner for Human Rights (OHCHR) estimates that a total of 41 Ukrainian children have been killed since Feb. 24 when Russia invaded, but Ukraine's Commissioner for Human Rights Verkhovna Rada is saying that a higher number of children have been killed, 71, and more than 100 injured as of Thursday.