If I understand the article correctly, the mother says the stock photo company "stole" it from her blog. Reading between the lines though, it would seem more likely that a "contributor" stole the image online, faked a MR and uploaded it as their own.

Obviously, it could be an agency, just not as likely as a rogue "contributor" who has no reputation to protect.

Then there is that whole flimsy "don't show the model in a bad light" clause most of the agencies have in their contracts with buyers. There is simply no way the agencies have the will or the capacity to ensure their buyers apply a modicum of common sense before using an image in a particular context.

No matter how the company got hold of the image or how aggrieved they may feel if it was supplied illegally, did they not think to check back with the agency around how they intended to use the image of a child? Did it occur to nobody that perhaps this was a sensitive use and that they'd better think twice about the context of the usage?