Mohammed Kutkut, 14, right, covers his face Saturday as he sits next to the name sign of his killed friend Ahed Qaddas in the Fakhoura boys school in Jebaliya, northern Gaza strip.

Gaza City, Gazy Strip ? Tens of thousands of children returned to schools across Gaza on Saturday after three weeks of war, playing games for some relief from the devastation and telling friends and teachers about the explosions they heard and relatives they lost.

In one classroom, signs with the names of three 14-year-old boys killed in the fighting were set on their desks — and their deskmates sat with stunned expressions next to the empty seats as the teacher encouraged the class to talk about their experiences.

“It’s very hard when one used to see 30 students in class, and after what happened, I see 27,” their teacher, Bassam Salha told the class at the U.N.’s Fakhoura Elementary school. “We lived three weeks in sadness. I want you students to help me to get out of the sad mood I am in now.”

Meanwhile, an Israeli foreign office official said President Barack Obama’s newly appointed special envoy to the Middle East is expected in Israel on Wednesday for talks on reviving Mideast peace negotiations after the Gaza fighting and on ensuring an arms blockade on the territory’s Hamas rulers.

George J. Mitchell will meet with Israel’s prime minister and other leaders, as well as the Palestinian president and prime minister in the West Bank, the official said, speaking on condition of anonymity because there has not yet been an announcement from Washington. The White House and State Department declined to comment.

Also Saturday, international aid organizations called for the unfettered entry of humanitarian and building supplies into Gaza. The territory’s borders with Israel and Egypt have remained largely closed since a cease-fire took hold earlier this week, though supply convoys have been able to come through.

In Israel, the defense minister was to propose to the Cabinet today that the government provide “moral and legal support” for officers in potential court cases related to the war’s conduct.

The reopening of schools, a week after a tentative cease-fire, marked a small step back to normalcy for Gaza’s 1.4 million residents. Israel had launched a 22-day air and ground assault, aimed at stopping rocket fire by Gaza militants on southern Israel.

Some 280 children were among the 1,285 Palestinians killed in the offensive, according to the Palestinian Center for Human Rights. Thirteen Israelis, including three civilians, were also killed during the fighting.

Israeli Prime Minister Ehud Olmert has expressed regret over the deaths of civilians, but Israel blamed the deaths on Hamas, saying its fighters used civilians, schools and mosques to shield themselves.

The scores of schools run by the United Nations — which are attended by 200,000 children — reopened along with Gaza’s public schools, which Hamas has run since seizing the territory in 2007.

“Getting these children back to school was our absolute priority,” John Ging, Gaza head of the U.N. agency that cares for Palestinian refugees, told the Associated Press.

In one school, first-grade girls with white ribbons in their hair swept shattered glass from the courtyard. More than 30 U.N. schools were damaged in the fighting.

The schools were also used as makeshift refuges by tens of thousands of Gazans fleeing clashes between Israeli forces and Palestinian militants in border areas, and by others whose homes were destroyed in the fighting.