A third child has died following Sunday morning's house fire in Carpentersville, Illinois. 

The fire happened around 9:43 a.m. in the 1700 block of Kingston Circle. When crews arrived, four people were in the burning home, but it was too late to save the other two boys inside. 

The 1-year-old was taken to Advocate Sherman Hospital in Elgin for treatment, but later died.

A family friend confirmed that all three kids were sleeping and trapped in the basement when the fire started.

The fire spread so quickly that it appeared by the time firefighters arrived on the scene, the home was fully engulfed in flames.

The friend confirmed the identities of those boys—2-year-old twins Jayden and Kayden and their 1-year-old brother Xander. 

According to officials, the boys' grandmother, her boyfriend, and the children's father were inside the home at the time. 

Animals were also inside the home. Two of the family's dogs also died in the fire.

Members of the Bureau of Alcohol, Fire, Tabacco, and Explosives and the state fire marshall were on the scene in the hours after that fire was extinguished. Police and the Kane County Coroner's Office are also performing their own investigations. 

"You can only imagine the loss of a child versus three children," Carpentersville Police Chief Todd Shaver said. 

Willam Lopez and his wife, who live across the street, said they saw the fire and ran to the house knowing the three boys slept in the basement.

"My wife, she wanted to go in there. I've never seen her move that fast," He said. "She ran and made it all the way to the garage, and when I pulled her back, I saw how high the flames were, and the smoke was like, wait, we can't go in there. It's going to be bad, you know?"

He continues, "It's hard, man. We feel like we could've went in there and done something more, you know."

Devastated family speaks at vigil

At a vigil Monday night, hundreds of strangers gathered outside the family's home and recited the rosary for three brothers. Some bringing candles to the scene of the deadly house fire.

The rhythm of the prayers was punctuated by a mother's mourning.

"Don't leave without saying goodbye," said the boys' mother, Josephine Beauchane, "because you don't know if it's going to be your last time."

Beauchane described her youngest son's last moments.

"I felt his heart stop," she said, "and I watched as he took his last breath, and I had to sit there and listen as the doctors told me that that they won't be able to save him anymore."

The boys's grandmother was also hospitalized for smoke inhalation, but has now been released.

"She tried so hard to save those kids. She kept running into the house, trying to find those children. She could not find them," said Christine Castillo, the children's paternal great-grandmother. "The smoke was too, too strong. She couldn't even scream out their name.

Investigators said it was too early as of Monday night to know what caused the fire.

"I can't imagine going into a fire and finding children," said Michael Beauchane, the boys' maternal grandfather.

The family said 1-year-old Xander was always happy, and the twins seemed to share a language of their own. They searched for something, anything that could be a silver lining.

"I always wanted to bring people together. I wanted to make everybody happy. I wanted to fix the world," said Josephine Beauchane, "and so far, it seems like that's what they did. They made this community stronger and brought everyone together." 

During a news conference Monday afternoon, officials said the cause of the fire remains under investigation but said the home did have working smoke detectors. The apartment is inhabitable and suffered $350,000 in damages. The village social worker has been working with the family. 

The village president says in the coming days, he will assist in organizing how to help the family.

There are already several fundraisers for the family. CBS News Chicago is told the fundraisers have collected tens of thousands of dollars in just the past two days.  

Anyone with information about the fire is asked to contact the Carpentersville Police Department at 847-551-3481.