One other passenger, a 38-year-old man believed to be the children's father, suffered only a broken thumb. He told authorities his wife was driving.
The accident happened Friday on North Livermore Avenue just north of Interstate 580 at about 7:30 p.m.
``It appears that they blew a tire crossed the double yellow lines, hit a tree, crossed back over, possibly flipped over and became fully engulfed in flames,'' said Sgt. Rich Luciano of the California Highway Patrol.
Authorities said firefighters arriving on the scene found a man at the side of the road sobbing, ``I've lost my family.''
Identities have not been released.
Luciano said he couldn't recall a worse accident. ``Nothing like anything like this with six children...I'll just say it's difficult from everybody,'' he said.
Rescue workers reported smelling alcohol on the man's breath, police said.
He told authorities he had crawled out of the van.
The crash remained under investigation on Saturday.
The woman was found outside the van and the children, ages 4 to 15, were found inside the blaze after the fire was extinguished.
The injured man was taken to a nearby hospital where he was treated for minor injuries and shock.
Authorities said the accident was discovered when a rancher called to report a fire near his property.