Children up and down the country dressed as their favourite authors for the occasion, but Myleene's kids went as their mum.
The former Hear'Say singer has penned several of her own books, including one on pregnancy and an another on crafts for kids, and Ava and Hero seemed more than happy to emulate her.
For their costumes, the girls wore matching leopard print jackets, skirts, tights and Fedora hats. In a close-up picture of Ava, she is clutching a coffee cup, a Myleene Klass book and is wearing over-sized sunglasses.
Definitely a right pair of mini-mes!
Sharing the snaps on Instagram, Myleene posted a 'crying with laughter' emoticon face, adding: "OMG my #worldbookday #daughters."
Meanwhile, Myleene wasn't the only celebrity getting involved in World Book Day. \
Britain's Got Talent judge and children's book author David Walliams spent the day flying around the country in a helicopter visiting various primary schools.
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