There's A Walrus In My Bed! by Ciara Flood 

Tonight, for the first time, Flynn is going to sleep in a proper big boy bed. But when bedtime rolls around, he just can't get to sleep. The reason? There's a walrus in his bed, of course! Mum and Dad play along while Flynn gives "Walrus" blankets, snacks, milk and a top-secret trip to the toilet, but it doesn't look like anyone is getting much sleep tonight.