Police said the collision happened just before 2 p.m. in the 2600 block of Thousand Oaks Boulevard.
According to police, the woman and her four children, three walking and one in a stroller, were in a crosswalk controlled by traffic lights as the van approached them. The woman was able to push the stroller out of the way in time before she and her three other children were struck.
One child was seriously injured and was transported to Los Robles Hospital and Medical Center. The mother and two children suffered less serious injuries. They were treated at the scene and transported to Los Robles as well.
A bystander held the child in the stroller until child protective services showed up.
The driver of the white van was taken into police custody.