The vigil was held at Cicero's Liberty Elementary School, where 5-year-old David Castellanos III attended as a kindergartner until his death Tuesday.
"Our hearts are definitely broken. Our students in the classroom are trying to understand how their friend David isn't coming back," said Jamie Georges, the boy's kindergarten teacher. "They want the family to know that they loved David as 5-year-olds love each other."
RELATED: 5-year-old boy, grandfather killed in Cicero apartment fire identified
The boy died overnight Tuesday when a house fire ripped through the second-floor apartment he lived in with his father and his 61-year-old grandfather, David Castellanos Sr.
David and his grandfather were trapped in the apartment building in the 4700 block of West 12th Place. They were found in the same unit on the second floor.
"Our day on Monday ended in the principal's office, which isn't always a good thing," said Liberty Elementary School Principal Robert Mensch. "David went over and gave Dad a nice big hug and said, 'I love you, Dad.' I'm going to remember that. I'm going to remember David and Dad and the love that they had."
Investigators were finally able to get back into the burned out home Wednesday, ruling out arson. But investigators are still unable to pinpoint the exact cause of the fire.
"What we're doing now is, we're in the basement. We're looking for a couple of things specifically, and then we're going to work our way up upstairs to the second floor," said Cicero Fire Department Chief Dominic Buscemi. "I would like to get something by this evening so we can get some closure to this and some closure to the family as to what happened."