The case comes as Southern California grapples with a rise in homelessness amid soaring housing costs.
The family had been living in the van for some time and relatives were aware of the situation but the father did not seek help, Whitney said.
"What is tragic about this is we have our special resources teams that have connections to different resources," Whitney said. "We don't want these people living in their cars, and especially with small children. We want them to be off the streets for their own safety."
Police declined to release the names of the victims until their identities were confirmed by Orange County Coroner investigators.
The family had been dead for at least two or three days by the time police arrived and the van was not running, Whitney said.
A clerk at the CVS store declined to comment early Friday. The strip mall — which also has a tea house, shoe store, pizza shop and mobile phone retailer — is located at a busy intersection in the city of 175,000 people about 50km southeast of Los Angeles.
- AP