Police say the child walked into the garage where the three pitbulls are kept around 8:45 a.m. Thursday when the animals attacked.
The child was severely injured and later pronounced dead at a hospital. Police say two adult relatives and a young sibling were home at the time. The Contra Costa County Animal Services department is assisting in the investigation.
The child's death comes amid a recent series of pitbull attacks that have renewed calls to put restrictions on owning the breed, which was developed for fighting.
One person was killed and three others hurt in a pit, CBS affiliate WREG reported Tuesday.
A 71-year-old man was attacked by two dogs while walking from one yard to another. He died after being taken to the hospital.
When firefighters arrived on the scene to treat the man, two of them were attacked. They were treated at a local hospital and then released.
A woman, reported to be the dead man's daughter, was also injured.
The owner of the dogs was arrested this past weekend for violating the sex offender registry act.
Some communities, like Worcester, Mass., are moving to crack down on such attacks.
The Worcester City Council on Tuesday gave preliminary approval to an ordinance that imposes tighter restrictions on pitbull owners. A final decision will be made next month.
The law requires pitbulls to be leashed and muzzled when not on their owner's property.
It also requires pit bull owners to place a warning sign on their property and notify authorities if their dog injures or threatens a person or animal.
Councilor William told The Telegram & Gazette that while 2 percent of the dogs licensed in the city are pitbulls, 25 percent of all reported dog bites were caused by the breed.