GAZA CITY (CNN) -

The boys were cousins -- playing, as they had many times before, at a beach by the sparkling waters of the Mediterranean when the shelling started.

The first shell struck a fisherman's hut on a jetty by the beach where the boys' game had taken them.

As a plume of smoke rose from the blast, several of the boys dashed across the sand, seeking cover.

But they couldn't outrun the second shell, which whizzed in and exploded right by them.

The attack on the Gaza City beach killed four boys, aged between 9 and 11, from the extended Bakr family.

Their names were Ismail, Zakaria, Ahed and Mohamed.

Growing child death toll

The Israeli military said the case is being carefully investigated and that preliminary results indicate the intended target of the strike was "Hamas terrorist operatives." It described the civilian deaths as "a tragic outcome."

But children have frequently been among the victims of the conflict between Israel and Hamas. Of the more than 200 people killed in the 10 days of Israeli bombardment of Gaza, around 40 are children, according to the United Nations.

Killings of the young also played a prominent role in setting off the confrontation.

Tensions in the region soared when the bodies of three kidnapped Israeli teenagers were found in the West Bank on June 30. Two days later, a Palestinian teen was abducted and burned alive in an apparent revenge attack in Jerusalem.

Journalists witness shelling

The deaths of the four boys on the Gaza beach Wednesday was a particularly stark example of the innocent lives lost in the fighting.

They died within eyeshot of a hotel housing several international journalists, some of whom joined in efforts to help people who were wounded in the shelling.

Veteran reporters described the harrowing scenes.

Nicholas Casey, a correspondent for the Wall Street Journal, said that after hearing a blast nearby, he went downstairs and saw bodies being carried from the scene, including one boy of around 9 or 10.

"His body was fairly mutilated and he was burned, his leg was twisted," Casey told CNN's Jake Tapper.

Another journalist said he had spent time playing with the boys.

"Minutes before they were killed by our hotel, I was kicking a ball with them," NBC News Foreign Correspondent Ayman Mohyeldin said on Twitter.

The boys had apparently been told by their fisherman parents not to go outside amid the recurrent Israeli aerial attacks. But the urge to stretch their legs in the sunshine was too strong.