Children held in overcrowded cells for weeks. Children sleeping on concrete floors because there aren’t enough mattresses. Children in filthy clothes with no showers, soap or toothbrushes. Children as young as 8 put in charge of infants because there’s no one to take care of them.

There’s no mystery why our taxpayer-funded detention camps for immigrant children are such a cruel, appalling mess. They’re run by agencies that were never designed to take care of kids, overseen by an administration bent on punishing illegal immigrants to produce an imaginary deterrent effect.

But the explanations don’t excuse the horrifying details that have trickled into view despite the Trump administration’s efforts to hide them.

First came lawyers’ reports from the Border Patrol facility in Clint, Texas, saying children in overcrowded cells were being denied soap and toothbrushes. Acting Homeland Security Secretary Kevin McAleenan, in reflexive denial, dismissed the accounts as “unsubstantiated allegations regarding a single Border Patrol facility.”

Except they weren’t. Only a few days later, his department’s internal watchdog reported that the problems were widespread.

“Children at three of the five Border Patrol facilities we visited had no access to showers (and) limited access to a change of clothes,” the inspector general wrote. Overcrowding in adult and child facilities “represent an immediate risk to the health and safety of DHS agents,” he added.

And the horror stories keep coming.

A Texas pediatrician who visited a warehouse holding more than 1,000 children said she found “a baby who’d been fed from the same unwashed bottle for days; children showing signs of malnutrition and dehydration” and poor sanitation “tantamount to intentionally causing the spread of disease.”

The United Nations high commissioner for human rights, Michelle Bachelet, said she was “deeply shocked that children are forced to sleep on the floor in overcrowded facilities, without access to adequate healthcare or food,” and added that the conditions may violate international law.

A Justice Department lawyer argued in court that the federal government isn’t legally required to provide child detainees with soap, dry clothing — or sleep.

Some of these accounts may turn out to be exaggerated. President Trump naturally dismissed them as “a hoax.” But no one has refuted the reports from the Homeland Security Department’s inspector general, which list violations of the government’s own standards in painstaking detail.

“My explanation is that it’s an extraordinarily challenging situation,” McAleenan said this week.

That’s not much of an explanation. Here are others:

First, the surge of illegal immigrants and asylum seekers, including thousands of children, hasn’t ended. Border Patrol officials say their detention facilities can hold 4,000 people at full capacity. At the end of June, they held an estimated 12,000.

Second, the administration’s “family separation” policy, which Trump publicly canceled amid bipartisan uproar last year, has continued in stealth mode.

Children are no longer routinely separated from their parents, but children traveling with other relatives — siblings or grandparents, for example — still are. “They’re just not a family unit,” Border Patrol enforcement chief Brian Hastings said at a recent Senate hearing.

Third, the Border Patrol is a law enforcement agency, not a child care provider. It’s supposed to process children within 72 hours and then release them to relatives or send then to child care facilities administered by the Department of Health and Human Services.

But the HHS says it has no room, and the administration doesn’t want to release children to their relatives — so they’re stuck in the Border Patrol’s holding cells, tents and warehouses.

Some Border Patrol agents have acted heroically in this crisis, but others joined a Facebook group that posted racist and sexually degrading content, the latest sign of trouble in an agency long plagued by corruption and mismanagement.

Still, this crisis isn’t principally the Border Patrol’s fault. It’s the fault of higher-ups who warned of a growing crisis but failed to manage it well.

Trump has naturally blamed Democrats in Congress for the mess — mostly because they had the effrontery to demand policy changes before voting to spend more money on detaining immigrants or building his wall.

But the Democrats didn’t devise Trump’s publicly declared strategy of making conditions bad for migrants to deter them from coming. That didn’t stop families who fled vicious gang wars in Guatemala, El Salvador and Honduras in fear for their lives.

Finally, this shouldn’t be a partisan debate, even in an election season — but, of course, it is.

“The Democrats’ bad immigration laws, which could be easily fixed, are the problem,” Trump tweeted. On the other side, Democratic presidential candidates have been trying to outdo each other in supporting leniency for migrants who enter the country illegally.

Still, this isn’t about which immigration policy you prefer. You can espouse a border wall, family deportation and “zero tolerance,” as Trump does; but that doesn’t excuse cruelty to children, whether by incompetence or design.

On Independence Day, the president gave a speech praising the armed forces and extolling the wisdom of the founding fathers. He would have done better to heed Thomas Jefferson: “I tremble for my country when I reflect that God is just.”