Hundreds of children, at least one as young as nine months old, traveled 2,000 miles without their parents to a foster care center in East Harlem, according to New York City Mayor Bill de Blasio,

The children were separated from their parents at the U.S. border with Mexico as a result of the Trump administration's "zero tolerance" policy towards illegal immigration.

De Blasio told reporters after touring the facility Wednesday afternoon the children arrived at the Cayuga Centers facility infested with lice and bed bugs, sick with chicken pox, and struggling with mental health issues because of the stress and trauma of being taken from their parents.

"Come clean with the truth. Who are these children? How many are they? Where are they? What is happening here?" De Blasio demanded of the government, adding he hadn't been able to get specific information from leaders in Washington. "How is it possible none of us knew there were 239 kids here in our own city?"

More than 350 children in all have passed through the East Harlem facility since the family separation policy began last month. The Cayuga Centers have been placing them in foster care and providing day care. It's one of at least eleven organizations in the metro area that have contracts with the federal government to take in immigrant children.

The mayor said workers at the Cayuga Centers had received threats and that police would be increasing enforcement.

"They didn't create the policy. They are trying as professionals to help these kids. So it's misguided," he said, "Do not direct [your energy] towards people who are trying to help the children."

Mass outrage from both sides of the aisle over the separation of children from parents at the border forced the government to retreat from the policy Wednesday. President Donald Trump signed an executive order that would enable families to stay together.

But it is unclear how or when the 2,300 children who've already been removed from their parents since the policy began, including those in the tri-state area, will be reunited with their parents.