People generally go to a bookstore to buy brand new books, not books that have already been read by someone all the way through. That's what a library is for, to read books for free. Browsing through a book is one thing but to actually sit there in B&N and read the book all the way through is wrong especially if pages get wrinkled, stained, etc.
If she wanted to avoid library fines she could have taken the kids to the library and sat with them while they read the books there inside the library.
With all that said the thing about leaving her kids there in the store is terrible. If they would have gotten kidnapped then she would have been crying about her babies.
I used to be on a site called customers suck but I stopped going there often because of the extreme liberal mindset of most of the posters. I got a warning on my account by a moderator for advising a gay guy that he probably shouldn't have mentioned to the elderly couple at his restaurant that he'd been at a pride parade when they commented on his sunburn, and to expect them not to react badly was naive. This was seen as "attacking" him even though I didn't say whether being gay was good or bad, just that he probably shouldn't have told the elderly couple about it.
One story that came up again and again on those message boards was about just the type of situation in the article. Toys-R-Us has this problem on a constant basis, with parents thinking that it's a free daycare. Very small kids will be left alone in the Toys-R-Us store or even a toy section of a Wal-Mart and then the parents will be gone who knows where for over an hour. Book stores and libraries are also common places for people to dump their spawn. At least these parents aren't going the Casey Anthony route to get rid of their annoying kids so they can still have their own selfish life, but they're coming awfully close to it by exposing kids to a big kidnapping/runaway risk.