(UVALDE, Texas) -- For some of the officers who responded to the Texas school shooting, it was personal.
When gunfire rang out at Robb Elementary School in Uvalde, Texas, agents from Customs and Border Protection immediately responded.
Law enforcement sources tell ABC News Border Patrol agents' children were inside.
One CBP agent was shot, but is expected to make a recovery, sources said, one of at least a dozen agents -- both on-duty and off-duty -- who rushed to the scene.
"Risking their own lives, these Border Patrol Agents and other officers put themselves between the shooter and children on the scene to draw the shooter's attention away from potential victims and save lives," Marsha Espinosa, the Assistant Secretary of Public Affairs at the Department of Homeland Security, tweeted.
Nineteen children and two teachers were killed -- the second-deadliest school shooting in U.S. history.
CBP Rio Grand Valley section Chief Jason Owens told ABC News that BORTAC, the elite Border Patrol tactical team, also responded.
Many CBP agents live in Uvalde, CBP Commissioner Chris Magnus said in a statement.
"CBP responded immediately to the incident with local law enforcement," Magnus said in a statement Tuesday night. "Many of our local CBP personnel live in Uvalde; they call this community home, and they work to protect their families, friends and neighbors every single day."
Owens told ABC News it's a rare positive amid the tragedy.
"In the worst of times you also get to see the very best in people," Owens said. "And that's what I've seen time and time again in these communities in South Texas."