(CNN) -- A loaded handgun fell out of a student's pocket onto the lunchroom floor and discharged Tuesday, wounding him and two other kindergartners in a Houston elementary school, the school district said.
None of the injuries was considered life-threatening, Houston Independent School District spokesman Jason Spencer told CNN.
The school district and Houston police are investigating how the 6-year-old who brought the gun to school obtained the weapon, Spencer said. "It's a crime to make a gun available to a child."
The weapon discharged once, and the children may have been hit by bullet fragments, Spencer said.
Five-year-old Jarneshia Broussard, a student who witnessed the incident, told CNN Houston affiliate KTRK the gun "fell, and then it shot."
"We were by each other and then it shot and the little girl started crying," Jarneshia recalled.
The two boys and one girl, all of them kindergarten students at Ross Elementary School, were taken to a hospital and their parents were notified, Spencer said.
He did not know their specific conditions, but said "the prognosis is good for these kids."
The boy who reportedly brought the gun and a girl were wounded in the foot, Spencer said. The third student, a boy, was struck in the leg.
Concerned parents flocked to the school to check on their children, CNN Houston affiliate KTRK reported.
"We made a recorded call to every parent," Spencer told CNN.
In 2006-2007, the latest year in which statistics are available, nearly 2,700 students nationwide were expelled or disciplined for bringing a gun to school, said William Modzeleski, associate assistant deputy secretary for the U.S. Department of Education's Office of Safe and Drug-Free Schools.
About 15% of them were elementary school students, Modzeleski told CNN. Those numbers track the previous year's numbers, he added.
"It's a school, community and a family problem," the official said. "If you bring a gun to school, this is a crime."
In elementary school situations, the student might bring a gun in for "show and tell" or it might have been left in a backpack by a parent or stepparent, Modzeleski said. Parents must ensure a weapon is secured at home, and not simply hidden, he said.
The problem can be found in schools everywhere, he said. "We have to get kids on board" to solve the problem, Modzeleski said.
According to a U.S. Centers for Disease Control and Prevention survey, from 1993 to 2003 there was a decrease in the percentage of high school students who reported carrying a weapon on school property at least once in the past 30 days. There was no significant change between 2003 and 2009.
Many schools are pushing prevention and other methods, such as random "wanding" of students with hand-held electronic devices to detect metal, because pass-through metal detectors are costly to staff, are labor intensive and take away from time for teaching, Modzeleski said.
Houston Police will lead the investigation into Tuesday's incident.
The school district had three cases of students bringing guns in the last school year, all at elementary schools, Spencer said.
"We are asking principals to remind (parents to check) where the guns are in their house," the spokesman said.
CNN's Phil Gast contributed to this report.