(CNN) Hours before a 3-year-old boy was found sleeping alone on a porch, police say the rental car that his parents were driving was burned and human remains were found inside.

Police in Buffalo, New York have been searching for the boy's parents since he was found Monday morning. The boy was wrapped up in a blanket inside a cardboard box that had been left out for cats, CNN affiliate WIVB reported. He was wearing only a diaper, the affiliate said.

"He is a very sweet boy, and he gives a lot of hugs and kisses," his grandmother, Zenaida Colon, told the affiliate.

The mother, father and a family friend of the child were traveling from Florida to Buffalo in a white Chrysler Pacifica SUV and were expected to arrive Sunday evening, Buffalo Police Captain Jeff Rinaldo said.

The parents Nicole Merced Plaud, 24, and Miguel Anthony Valentin-Colon, 31, as well as their friend 29-year-old Dhamyl Mirella Roman-Audiffred, are considered missing persons.

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