The driver of the 2016 Volvo S60, which careened out of control after striking the pedestrians and crashed, was also taken to a hospital and remains under investigation, according to police. The driver’s license was suspended Tuesday, according to Brooklyn city councilman Brad Lander.
The deadly incident occurred about 12:40 p.m. at a bustling intersection in the Park Slope neighborhood of Brooklyn, police said.
Police were investigating whether a medical condition contributed to the crash.
Miles was carrying her 4-year-old child and her friend, Lauren Lew, was pushing her 1-year-old child's stroller when they were hit, witnesses told police.
The children were identified by police as 1-year-old Joshua Lew and 4-year-old Abigail Blumenstein. Both children lived just blocks from where the crash occurred, police said.
Miles won a Tony for her performance in the 2015 Broadway revival of "The King and I."
"This is in support of Lauren Lew and her family, who were also struck by yesterday's tragedy, along with @RuthieAnnMiles. Unimaginable. Help if you can," Miranda tweeted.
The preliminary investigation indicated that the 44-year-old woman driving the Volvo "failed to maintain control of the vehicle" as she headed west on Ninth Street and hit the pedestrians at Fifth Avenue in a busy commercial area, police said in a statement.
“It’s really, really sad what happened today,” de Blasio said.
“This loss of life is tragic and painful for all of us, particularly those of us who are parents,” he added.
De Blasio was confronted Tuesday morning by protesters demanding safer streets as he arrived to work out at a YMCA, less than a block from where the fatal incident occurred.
Police said the two children and their mothers, ages 33 and 34, were transported to nearby Methodist Hospital. A fifth victim, a 46-year-old woman, was also taken to the hospital by paramedics, police said. The injured victims were in stable condition.
The driver of the car, who was not immediately identified, was taken to NYU Langone Hospital in Brooklyn, where she was also in stable condition.
"Ruthie is beloved by her many friends and colleagues in the Broadway and touring communities. She is always kind and always has a smile. It is our honor to help her in this difficult time," Jack Stephens -- who was the company manager on "The King and I" -- wrote on the GoFundMe page he established for Miles.
On the GoFundMe site for Lew's family, friends wrote, "While there is nothing we can do or say to bring their boy back, we hope these funds will serve as an expression of the community supporting them during this time."
ABC News' Meghan Keneally contributed to this report.