It’s not just the kids at the border.

America systematically shortchanges tens of millions of children, including homegrown kids. American children are more likely to be poor, drop out of high school and die young than in other advanced countries.

We tear apart homegrown families through mass incarceration, excessive juvenile detention and overuse of foster care. One black child in 10 spends time in foster care — and 61,000 foster kids went missing since 2000.

Like immigration, mistreatment of children is an old problem President Donald Trump exacerbates. Shortages and when priorities conflict.

“A shockingly high number of children in the U.S. live in poverty,” the United Nations special rapporteur on extreme poverty and human rights, Philip Alston, declared in a scathing report. Almost one-fifth of American children live in poverty, and they account for more than one-fifth of homeless people.

Alston told me “there’s a very direct link” between the mistreatment of immigrant children and indifference toward low-income children across the country. The core reason, he suggested, is lack of compassion.

Nikki Haley, the U.S. ambassador to the United Nations, protested the U.N. report, saying, “It is patently ridiculous for the United Nations to examine poverty in America.”

Really, Ambassador Haley?

Yes, it’s weird a U.N. official tasked with poverty investigates the most powerful country in the world — and finds children here have worms. I’m glad the U.N. speaks up not only for impoverished children in Congo, but also for those in, say, South Carolina, where a newborn black child has a shorter life expectancy than a child born in China.

Two researchers, Kathryn Edin and Luke Shaefer, found some 3 million American children live in “extreme poverty,” with a cash income of less than $2 per person per day, the global metric for extreme poverty.

That’s not to say poverty in America is comparable to that in poor countries. American children may go to bed hungry, but very few are stunted from malnutrition, compared with 38 percent of children in India.

The paradox is that the United States historically was a safe and nurturing place for children. America helped lead the world in mass education, and in 1960, children here died at lower rates than most other advanced countries.

Since about 1970, however, as other countries provided universal health care and built social safety nets, American children died at higher rates. A child is 57 percent more likely to die by the age of 19 in the U.S. than in peer countries, according to a study published this year in Health Affairs.

Half a million American children suffer from lead poisoning each year. Dr. Peter Hotez, a tropical disease specialist at Baylor’s College of Medicine, warns that here in the United States, “Millions of children living in poverty may be affected by toxocariasis, a parasitic roundworm infection.”

Why do we stiff children? Why do we provide universal health care for senior citizens (expensive)but not for children (cheap)? The simple answer: They don’t vote. They depend on us, and we fail them.

If we can broaden the outrage to the plight of all children in America, we could transform lives.

In Arkansas, I once dropped in on the home of a struggling 13-year-old boy. It was a filthy flophouse for drug users in a gang-ridden area. There were no books or food; the only reason the power wasn’t cut off was the pit bull that scared the utility crew.

These are difficult problems but not hopeless ones. We know what works. Early childhood programs make a huge difference: parent coaching, high-quality prekindergarten, lead poisoning interventions, social worker visits, and mentoring.

World Bank President Jim Yong Kim cites a study indicating if the U.S. invested in effective early childhood programs, the lifelong benefits would be so transformative that American inequality could be reduced to Canadian levels.

We already have a model: When Tony Blair was the British prime minister he cut child poverty nearly in half with a major campaign.

Unfortunately, Trump is moving in the opposite direction, cutting benefit programs in ways that hurt poor children. Trump’s tax cuts add to the deficit — we’re sticking children with the bill.

A national, bipartisan outcry forced Trump to back down from tearing immigrant children from parents at the border. Now we need a similar outcry on behalf of all of America’s children.

— Nicholas Kristof is a columnist for The New York Times.