The girl was a student at P.S. 89 in Elmhurst, Queens.
They were taken by ICE last week after a routine immigration check-in at 26 Federal Plaza.
"No child or family should be uprooted from their community or feel forced to hide in the shadows," said New York City Public Schools Chancellor Melissa Aviles-Ramos. "This is a child that should be preparing to go back to school this fall, where they are cared for, valued, and - most importantly - safe."
The girl's 19-year-old brother was also picked up. He remains in ICE custody at Delaney Hall Detention Facility in Newark, New Jersey.
Eyewitness News has reached out to the Department of Homeland Security, but have not yet heard back.
The 6-year-old was the first known ICE arrest of a New York City child under the age of 18 during President Donald Trump's immigration crackdown.
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