Boston Children’s Hospital had a wave of young patients brought in on stretchers Monday, all hurt by bombs detonated on a sunny day amid spectators of the city’s famed marathon.

One was a 2-year-old boy with a bleeding head injury, who was admitted to the surgical intensive care unit. Another was a 9-year-old girl with a leg trauma so severe that she spent hours in the operating room.

Law enforcement officials said an 8-year-old boy was among the people killed in the explosions near the finish line.

In all, nine children were admitted to Boston Children’s, youngsters who typically visit a physician only with their parents and to be treated for a seasonal flu or Strep throat. But these were bombing victims, including a 14-year-old boy with a head injury, a 10-year-old girl with a leg fracture, a 12-year-old with a broken femur, and a 7-year-old boy with a leg injury. Three other children were treated in the emergency room for minor injuries along with a 42-year-old parent.

At nearby Massachusetts General Hospital, 22 adults were admitted. Six were in critical condition. Four had to have their legs amputated, the hospital reported.

Massachusetts General’s emergency medical physician, Alasdair Conn, told television reporters that the injuries were more akin to those from a battlefield, not a spectator viewing stand.

The injuries had put several Boston hospitals on high alert, and pulled dozens of emergency room physicians on call. Seven hospitals were handling the more than 100 people who were injured.

As of late Monday, 23 patients had been admitted to Boston Medical Center, two of them children. Sixteen of those patients were listed in serious condition.

“We have activated our Incident Command System and are working closely with the local officials,” said Meghan Weber, a spokeswoman for Boston Children’s Hospital. “We are preparing to receive overflow patients from Brigham & Women’s Hospital.”

Alice Crites contributed to this report.

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