Officers responded to reports of a crash involving pedestrians on Calistoga Road at Marit Drive at around 6:05 p.m., according to Santa Rosa police.
Arriving officers found a 15-year-old boy and a 14-year-old girl who had been struck in a crosswalk by an SUV. The vehicle's driver was 49-year-old Almir Dafonseca of Sebastopol.
The boy was taken to a hospital with serious injuries, police said. The girl suffered moderate injuries and was also hospitalized.
Dafonseca stopped at the scene, police said.
Alcohol or speeding does not appear to be a factor in the crash.
Calistoga Road between state Highway 12 and Dupont Drive was closed until 10:30 p.m. while police investigated.