It was a school bus loaded with kids, aged 5 to 15, headed to a park in Oakland as part of their summer day camp experience.
The bus suddenly crashed into a van in front of it on I-80 and none of the children were wearing seatbelts.
The crash set off a chain reaction that involved six other cars, an accident that prompted a large-scale response from emergency personnel.
"They had multiple drivers who had sustained injuries. Fire was called to the scene. They immediately set up a triage, classified the injuries, most of them being minor injury," CHP Sgt. Melissa Kittell said.
The CHP reports 19 kids and adults from Camp Kee Tov and the bus driver suffered minor injuries, mostly bloody noses and bumps and bruises.
Four others, drivers in other cars, were also treated at area hospitals.
"We had a total of 23 patients that were transported and an additional 17 that were not injured," Berkeley Fire Department Asst. Chief Abe Ramon said.
California law requires buses built after July 1, 2005 to be equipped with seatbelts. The older Berkeley Unified School District bus involved in this accident did not have seatbelts.