As other students rushed to safety, their parents beat three of the four gunmen unconscious.
Four attackers stormed Siem Reap International School at around 9 a.m., grabbing children from at least 15 countries and demanding money, weapons and a vehicle.
Gunfire broke out inside the school, and hostage takers later told police they killed the 3-year-old Canadian boy because he was crying too much. Police moved in after they "threatened to kill the other children one by one," Information Minister Khieu Kanharith said.
Authorities said they managed to talk the attackers out of the building after giving them a minivan and $30,000 in cash. When the men got into the vehicle with four children, security forces closed the gate to the school compound and launched an assault, yanking the men from the van.
"They tried to shoot at the police with their AK-47. Apparently, the gun jammed, and at this point, the police came, smashed the windows, and arrested the four hostage takers," Liam Cochrane, managing editor of the Phnom Penh Post, told CBS Radio News.
They later described themselves to police as penniless, saying they had decided to prey on the children of rich foreigners after they failed to find work.
Nearly 40 children, some as young as 2, rushed past the school gate and into the arms of their panic-stricken parents — some of whom charged the hostage takers, beating three unconscious. Police shielded the fourth. All were taken into custody.