The National Library Board (NLB) took some heat last week after it had to withdraw from circulation a series of eight Malay-language children's books found to have controversial content.

One of them has, on its cover, smiling children wearing the Jewish skullcap and holding machine guns. Another book has a picture of a Muslim boy wearing what appears to be a suicide vest, surrounded by masked adults. These came to light only after a Twitter user posted photos of the books online. NLB is now reviewing another 130 titles by the same Malaysian publisher.

The episode raises a few concerns. First, the library has a tiered system of approvals before books are bought with public funds and put into circulation. It is within reason to expect librarians to pay more attention to books on race, language and religion. It would not have taken a librarian more than a day to read the eight books.

Second, the books were in circulation since 2013. It took too long for the alarm bells to ring.

Minister for Communications and Information Yaacob Ibrahim, whose ministry oversees public libraries, said the library did its due diligence, but it was not possible to vet every piece of reading material. He added that the Government and NLB will learn from the episode. NLB is reviewing its vetting process for sensitive and divisive content.

The episode shows that Singaporeans are sensitive to issues that can hurt social harmony and are speaking up about it. Of course, one can also argue that the Twitter user ought to have raised the matter directly with NLB instead of going public, which risked upsetting more people.

More importantly, it is a reminder to parents to pay attention to what their children read. This includes not just the content in library books but also what is easily found online.

More vigilance on the part of public officials, the public and parents cannot hurt, especially on matters of race, language and religion.