A man, woman and two children, ages 3 and 4, were hit by a Cadillac headed north on Foster Road near Interstate 10 around 5 p.m. Thursday, accident investigators said.
A mangled stroller could still be seen at the crash site an hour later.
Bexar County Sheriff's investigators believe the four were a family.
The 31-year-old father was killed by the impact. The mother, 35, was rushed to San Antonio Military Medical Center while the two children were taken to University Hospital.
The 38-year-old female driver might have been distracted by her cell phone before the crash, investigators said.
"We have witness statements that say she was on the phone, so we confiscated it and will look into that to see if anything happened there," said Sgt. E.M. Conger.
A witness stopped to help the victims and administer CPR.
There has been no word on what charges -- if any -- the driver could face.