Samar Hamdan ran weeping through the street, trying to touch the body of her dead 11-year-old brother during a funeral procession in this northern Gaza town.

Just a day before, the 15-year-old girl's two sisters were also buried, victims of the same strike from an Israeli missile.

As Israel steps up its attacks on the Hamas rulers of the Gaza Strip, one of the most densely populated spots on Earth, children are paying the price.

"In this crowded strip, everything is beside everything else," said Karen Abu Zayd, a top U.N. official in Gaza.

Israel says it is only targeting Hamas militants and the rockets they send streaking into southern Israel. More than 400 Palestinians have been killed in the strikes, many of them members of the Islmaic militant group's security forces.

But at least 37 children and 17 women have died, according to the Hamas-run Health Ministry. The United Nations has said the death toll includes 34 children.

With some 1.4 million Gazans crammed into a sliver of land 25 miles long and just 3 to 7 miles wide, military targets and civilians tend to exist side by side.

Israel says Hamas militants fire rockets from residential areas and schools, aware that the Israeli military response may cause civilian casualties.

"Hamas uses civilians as human shields," said an Israeli military spokeswoman, Maj. Avital Leibovich. "The targets we picked are military."

But the broad range of Israel's targets ? police compounds, fire stations, homes of militants, Hamas-run mosques and university buildings ? means most shelling is occurring in residential areas.

Israel's strike Thursday on the home of top Hamas leader Nizar Rayan was a typical case.

The bomb flattened the house and killed Rayan ? as well as 18 other people, including nine of his children, ages 2 to 19, and all four of his wives. Television footage showed medics clutching the bodies of children dug from the rubble of the house and neighboring buildings.

Hamas officials said Rayan, who sent one of his own sons on a 2001 suicide bomb mission that killed two Israelis, refused to leave his home even though he knew he was a likely target ? effectively putting at risk civilians living nearby.

For the Hamdan children, however, the attack was random. The three victims, Haya, 12, Lama, 4, and Ismail, 11, were dumping garbage in an empty field near their home Tuesday morning, not knowing that Gaza militants nearby had just fired rockets at Israel.

An Israeli warship fired a missile at the site. The two girls were killed instantly, but Ismail lingered on until Wednesday.

At his funeral, his sister Samar tried to follow his flag-wrapped body, until the mourners stopped and took her home to her devastated mother.

"My children are dead, why am I alive?" the mother wailed.