The boy's first request after being examined, police said, was a grilled cheese sandwich and a juice.
His mother, identified Wednesday as Kiana Workman, 38, of New York City's Brooklyn borough, was discovered dead Tuesday on the floor of her bedroom after maintenance workers at the apartment complex in northern New Jersey reported a foul odor. Because the chain lock was on, police said, the toddler couldn't get out.
Officer Joseph Sauer said the boy was naked but coherent and not crying when he kicked in the door and his partner lifted the youngster up by the arms and pulled him out of the overheated apartment.
"The only way to describe the little boy was it was like a scene from World War II, from a concentration camp, he was that skinny. I mean, you could see all his bones," Sauer told The Associated Press.
The apartment in this city 15 miles west of New York belongs to Workman's mother, who is recuperating from surgery at a nursing center, said police, who could not track down any other relatives.
The boy, now in state custody, remained in a hospital where he was being treated for malnourishment and dehydration, police said.
"Physically, he's fine. Whether there are any mental problems later on ... I'm not a child expert," Police Director Daniel Zieser said.
The boy was not strong enough to open the refrigerator and was unable to open a can of soup. Police said he told them he had been eating from a bag of sugar.
The boy could not say how long his mother had been dead.
Police said he put lotion on his mother, leaving behind handprints, in an attempt to help her.
Officer Sylvia Dimenna, who traveled in the ambulance with the boy and stayed with him at the hospital, said he was very bright and articulate but tired.
"He said he missed his mommy," she said.
Police initially estimated she had been dead five days before the discovery was made, but Zieser said Wednesday it may have been two to three. Nobody had talked to her for about a week.
The boy weighed 26 pounds, but at the age of 4½ should have weighed 40 pounds or more, Zieser said.
"It's possible he was improperly cared for before the mother's death; we just don't know yet," Zieser said.
Autopsy results that would help them better determine the time of death were pending. Police said they did not suspect foul play.
Police said they were getting calls from around the world from people offering to adopt the child or donate money or toys.
"It's overwhelming," Zieser said.
"I just hope everything works out for the child," the police director said. "We're just going to take it one step at a time and do the best that we can for the child."
Police said they were trying to find someone in the family capable of taking care of the boy, including a brother of Workman believed to live out West. But he said it would be up to the state's child welfare agency to determine where the child is placed.
Zieser described the apartment complex as a well-maintained property with few problems.
But he said everyone there "basically stays to themselves."