BOSTON — An 11-year-old California boy and a 9-year-old girl are in critical condition at Boston Children’s Hospital following the deadly bombings at the Boston Marathon. A 5-year-old boy is in critical condition at Boston Medical Center.

Aaron Hern, of Martinez, Calif., has undergone multiple operations, including three to four hours of surgery on Wednesday to further treat his badly injured leg, including removing shrapnel and damaged tissue. His 12th birthday is May 1.

Additional Photos

Dr. William Mackey, chair of surgery at Tufts Medical Center in Boston, describes the shrapnel removed from bombing victims to reporters at the hospital, Tuesday, April 16, 2013. Mackey was among the staff who treated the 14 patients injured in the bombing at the finish of the Boston Marathon who were treated at Tufts. (AP Photo/Josh Reynolds)

Boston Marathon runner Vu Trang, of San Francisco, cries at a makeshift memorial on Boylston Street near the finish line of Monday's Boston Marathon explosions, which killed at least three and injured more than 140, in Boston, Wednesday, April 17, 2013. The bombs that blew up seconds apart near the finish line left the streets spattered with blood and glass, and gaping questions of who chose to attack at the Boston Marathon and why. (AP Photo/Charles Krupa)

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The 9-year-old girl also has a severe leg injury.

Boston Medical Center won’t release information about the 5-year-old boy’s injuries.

Children’s Hospital says a 2-year-old boy with a head injury is improving and might go home Thursday.

The children were among more than 170 people injured in Monday’s bombing. Three people were killed.

No one has claimed responsibility for the attack.