8-year-old boy identified as 6th fatality in Wisconsin Christmas parade

In his first comments on the deadly crash, President Joe Biden said Monday, "While we don't have all the facts and details yet, we know this morning that five families in Waukesha are facing fresh grief of a life without a loved one."

"At least 40 Americans are suffering from injuries, some of them in critical condition, and an entire community is struggling, struggling to cope with the horrific act of violence," Biden said.

"Last night, the people of Waukesha were gathered to celebrate the start of a season of hope and togetherness and Thanksgiving," he continued. "This morning, Jill and I and the entire Biden family, and I'm sure all of us, pray that that same spirit is going to embrace and lift up all the victims of this tragedy, bringing recovery from the injuries and wrapping the families of those who died in support of their community."

The administration is "monitoring the situation very closely," Biden added.

-ABC News' Sarah Kolinovsky

The person being held by police is 39-year-old Darrell Brooks, multiple law enforcement sources told ABC News. Brooks has not been charged with a crime in connection with the parade incident nor has he been named a suspect.

-ABC News' Pierre Thomas, Josh Margolin, Luke Barr, Aaron Katersky

Ten of the 18 children taken to Children’s Wisconsin hospital were admitted to the ICU, including six children in critical condition, hospital officials said.

Three of the ICU patients are in serious condition and one is in fair condition.

Another eight patients were admitted in fair conditions and two of the 18 children have since been discharged, officials said.

The hospitalized children range in age from 3 to 16 and include three sets of siblings, officials said. Injuries include serious head injuries and broken bones.

Six children were sent to the operating room Sunday night and another two children will undergo surgery on Monday, officials said.

-ABC News' Josh Hoyos

Brayden Kowalski was at the parade in Waukesha, which he described as "a very loving community," when he "saw about a block away, the SUV hurtling towards me."

He pulled his nephews, ages 4 and 6, out of the vehicle's path at the last minute. The SUV was about 5 feet away, Kowalski said.

Kowalski said he "was fear-stricken, but I just, I tried the best I could to help," escorting people from the street over to the sidewalks.

Of the driver, he said, "I don't know if they were targeting people, but they for sure weren't dodging people. "