It happened in the 7000 block of Bissonnet around 7:05 a.m. The victim, Antonio Medardo Alvarenga, 40, was taken to the hospital in good condition.
Southwest Houston resident Joanna Perez said she's in disbelief over what happened.
"It's very shocking. It's very scary, very sad," Perez said.
Alvarenga was driving his son and daughter, also 10, to school when the boy shot the man through the back of his car seat, police said.
The boy is the best friend of Perez's son.
"Him having access to any weapon of any kind is shocking. How did he get it? I don't know. It makes me think constantly about what happened," she said.
While paramedics took Alvarenga to the hospital, police took the 10-year-old boy to the Children's Assessment Center for questioning. Police said he's now at the hospital.
"I just feel so bad for them, and I hope -- I don't know how they fix it. He's a great kid," Perez said.
No charges have been filed.