International law is a joke. If you knew anything about it you wouldn't be screeching "whataboutism!" at even the most obvious of comparisons, because you'd know that a cornerstone of what passes as International law is looking at practices of other countries.

But let's see what your article says:

Kherson was liberated in November after eight months of occupation, but is pounded every day and night by Russian artillery... A report last October by Yale University Human Rights Lab, citing a vast range of open sources in Russia and Ukraine, traces many reasons for their abduction: including so-called “evacuation” from state institutions such as that at Kherson

This article documents that (when it was written) Kherson was still an active war zone, but nevertheless adds scare quotes to "evacuation," as if there is no need to evacuate children from a war zone and this is all a Russian pretense. So early on we can see that no Russian explanation will be deemed credible, even when the explanation Russia gives (e.g., evacuation) is documented by the author himself.

“Staff hoped for three months that our army would somehow evacuate them,” Sagaydak continues, “but when it became apparent this would not happen, we made arrangements for those with living relatives

Even Ukranians recognize the need for evacuating children, but nope, it's an evil plot when Russia does it! Note also that the immediate evidence we have here -- an in-person interview with a Ukranian working with kids, not a second- or third-hand story -- mentions exactly what I said: kids orphaned by the war who need to go somewhere, not Russians snatching kids from their parents.

“Another woman here, aged only 30, took five, which could not possibly have been hers, so we made up a legend that she was helping her pregnant sister while she gave birth. We had to invent all the medical records, and worried when a driver turned up who was not the one we had planned. But when they were stopped, and the untrustworthy driver even told the true story, the kids managed to outwit the occupying soldiers.”

What is more believable: Russians are trying to snatch any kid they can lay their hands on, for some reason the Ukrainians subjected to this believe fake medical records will prevent this, a driver tells them "hey here's five kids with fake documents," and the kids outwit a bunch of soldiers with some unexplained cunning? Or is it more likely that Russians consider kids in a war zone basically a nuisance, and aren't particularly invested if someone is trying to evacuate them?

But then, on 15 July, the Russians returned, with 15 more children to be cared for

So the Russians are stealing children by... taking them to a Ukranian orphanage?