Its denigrators will be kicking themselves: a children's book about two male penguins who raise an orphaned chick has shot up Amazon's bestseller charts after it was named as the title which people have tried hardest to ban in the US.

And Tango Makes Three by Justin Richardson and Peter Parnell is a children's picture book based on the true story of a zookeeper at a New York zoo, who spotted two of his male penguins attempting to hatch a stone, and "realises that it may be time for Roy and Silo to become parents for real". Parents in the US have complained about its "homosexual undertones" (it's "a homosexual storyline that has been sugar-coated with cute penguins", said one) according to the American Library Association, which puts together a list of the most challenged titles in the country every year. And Tango Makes Three has topped that list for the last three years.

But the challenges appear to have had the opposite effect from what their instigators might have hoped. Renewed focus on And Tango Makes Three this week, thanks to Banned Books Week, the annual US celebration of the freedom to read, has sent it racing to the top of Amazon.co.uk's "movers and shakers" chart, which monitors books experiencing sudden surges in demand.

"The current boost in its popularity during Banned Books Week will only spread its positive message to more families," said Ingrid Selberg, children's director at the book's UK publisher, Simon & Schuster. "And Tango Makes Three is a charming picture book about love and family. We are proud to have it on our list."

Richardson himself said today that it was "regrettable that some parents believe reading a true story about two male penguins hatching an egg will damage their children's moral development". "They are entitled to express their beliefs, but not to inflict them on others," he added.