Twenty-year old Christian Perez is facing torture and child abuse charges stemming from the incident involving his girlfriend's 16-month-old son.
Firefighters found the boy unresponsive and convulsing after receiving a 911 call. He had severe burns over 70 percent of his body.
Perez's sister and brother-in-law are also in custody, facing felony child endangerment charges.
Police say the three didn't seek medical treatment for the child for two hours after the incident.
The baby is being treated at a Shriner's Hospital burn unit in Sacramento.