Janet and Allan Ahlberg are widely considered among the greatest of children’s authors: wildly successful, universally adored, and critically lauded (Janet was among a handful of children’s illustrators to have won the Kate Greenaway Medal twice). So I can hardly claim that their genius hasn’t been recognised.

However, there is a particular aspect to their work that stands out to me, and which has not, as far as I can tell, been discussed in the many articles written about them since Allan’s death last year. The delightful wordplay, the beautiful illustrations, the boundless creativity, have all been rightly praised, as has the inventive nature of their work, pushing the boundaries of the picture book medium with technical innovations such as the holes of Peepo!, or the adorably tiny envelopes and letters built into the The Jolly Postman.

But it’s another quality of their genius which has struck me over the many years that I’ve sat, reading and re-reading their books to highly sleep-resistant babies. And that’s the extraordinary level of effort and attention they put into creating a completely consistent and detailed world for every book.