Ever since news broke of the children separated from their parents at the US border, Big Apple residents have rallied around the kids.

Social-service agencies housing the separated children have been flooded with donations and offers from concerned citizens all over the city.

I’ve heard neighbors in my Brooklyn neighborhood talk about putting up spare bedrooms and donating diapers and toys. Local businesses have planned fundraisers and drives to deliver supplies to migrant children.

As a leader of one of the city’s oldest foster-care agencies in Brooklyn, I first felt frustration. What about New York City’s youths in foster care? They’re also wrenched from their parents — although to protect them from harm.

Each year, the Administration for Children’s Services removes about 5,000 children and teens in the five boroughs from their parents — not because of illegal immigration, but alleged abuse, neglect, drug use and domestic violence — throwing their lives into tremendous turmoil.

Of course, the separations may be justified, but New Yorkers should feel equally concerned about these kids who are bereft of parental care.

On any given day, about 130 of these children must stay in a boarding center while they await placement in a foster home. We don’t have enough homes to take in all the children in need.

Children are separated from their families and sometimes torn from their siblings. A few years ago, we had to place two sisters, ages 6 and 7, in different foster homes because the agency didn’t have homes with room for both of them.

Now those girls are being adopted by two different families. They won’t get to eat meals together, share their first days of high school, or say good night to each other before they go to sleep.

Our children are in deep pain because of these family separations.

We have five group homes filled with teenagers — 50 in all. The older youths tell us they don’t want to be in a group home. They want to be with a family.

We know from years of research that separation affects a child’s brain development and has long-term negative health effects. Toxic stress hinders learning and the ability to form connections with other people.

The only thing that can offset these effects is a strong bond with a committed adult, which is why being a foster parent can transform a kid’s life.

We, like all New York City foster-care agencies, are in dire need of safe and loving foster homes for our kids, donations for our programs and mentorships. We’re looking for people to open their hearts and homes to children and teens while they’re going through one of the most difficult experiences imaginable.

Make the migrant crisis a call to action, New Yorkers. If you’re willing to offer bedrooms to kids separated from their parents at the border, why not offer them to New York kids in our own back yard?

Dawn Saffayeh is the executive director of 150-year-old HeartShare St. Vincent’s Services in Brooklyn.