Noah Fake was tossed around, punched and beaten by his mom Robin Greinke, 26, and Steven Neil, 33, after he wet himself.
Orange County Detectives said the pair were drinking and possibly taking pills before the hour long attack which left him severely injured.
But although he was seriously injured Neil convinced Greinke to wait until the next day to call for help.
It was only when she noticed Noah wasn't breathing, they finally called 911.
Det Chris Dillon said: "The mother admitted, full confession, how they beat the baby and she was very apologetic, but obviously it's too late now. He's gone."
Deputies were called to the apartment on March 1, and doctors originally thought the child was sick with meningitis because of his bruises.
But the autopsy showed, however, that he had been killed by blunt-force trauma to his head.
Dillon added: "They explained how they tossed the little boy around. They were upset with him and they tossed him and spanked him and punched him."
It is not clear whether the child was ever abused before, but one of Neil's former girlfriends said he also beat them and his own biological child.
The disgusting pair have now been charged Neil and Greinke with first-degree murder, aggravated child abuse and child neglect.