At least six children's books have been pulled off the shelves in recent months, more than previously confirmed by the National Library Board (NLB).
Last Saturday, the library board's chief executive, Mrs Elaine Ng, said three titles - And Tango Makes Three, The White Swan Express and Who's In My Family? - had been pulled this year.
However, The Straits Times understands that there were more.
The NLB withdrew the children's book Who's In My Family? by Robie Harris on March 26, and then temporarily took all 22 remaining titles by Harris off the shelves in April.
They were then reviewed individually by the board's selectors, and three titles classified as non-fiction for junior readers were recommended for permanent removal.
These were It's Not the Stork!: A Book About Girls, Boys, Babies, Bodies, Families And Friends; It's So Amazing! A Book About Eggs, Sperm, Birth, Babies, And Families; and It's Perfectly Normal: Changing Bodies, Growing Up, Sex, And Sexual Health.
All three focus on sex education for children and have a page featuring various family structures, including those with single parents and same-sex couples.
The Straits Times understands that a note was sent out to all public libraries on April 8, asking for the three titles to be withdrawn. They are no longer listed in the NLB's catalogue.
All remaining titles by Harris, which were deemed "pro-family books for young persons", were returned to the shelves. These include Who Has What?: All About Girls' Bodies and Boys' Bodies, and Mail Harry To The Moon, a story on having a new sibling.
Yesterday, the NLB declined to comment on whether it had indeed withdrawn the three Harris titles and why it had done so.
The NLB may also have axed another children's title, The Family Book, by Todd Parr.
Transport consultant Paul Barter, 47, said on Facebook last Saturday that he wrote to the NLB that day to ask if it had removed the book.
He borrowed it several months ago, but cannot find it in the library now.
Dr Barter, who has an adopted daughter, said he has been looking for "age-appropriate books that have adoption as a theme, that mention adoption in positive ways or which portray a diversity of family circumstances in a friendly way".
He told The Straits Times that he had wanted to borrow the book again as it was a "useful resource to teach my daughter about her identity", but could not find it.
Again, the NLB declined to comment.
The Facebook group, Singaporeans United For Family, which collected signatures to support the NLB's action, has submitted an open letter to the Ministry of Communications and Information, Ministry of Social and Family Development and Ministry of Education.
According to the group, the letter is backed by 26,000 signatures. It declined to reveal the identities of these supporters, and would not name the person who had written the online letter.
Mrs Ho Bee Bee, a 42-year-old personal assistant who signed the letter, said the removed titles "were for kids of young age".
"Making them readily available at the children's section makes me uncomfortable," said the mother of two boys, aged 10 and 11. "I had trusted NLB to purchase books suitable for young children."