You can read what illustrator Lynne Chapman was thinking as she started work on the rough drawings for this first spread on her blog post at http://lynnechapman.blogspot.com/2009/06/opening-spread.html
This is her initial sketch of the little boy who's voice it is telling the story. He is looking rather anxious - he is thinking about those bears:
Lynne Chapman, illustrator of Bears on the Stairs, reads this page of the story to children at the Waterstones book launch. Behind her, the 'big, biffy' koala from the story has gone on his holidays to the seaside: a fantasy prompted by the children at the event.
This is a page from Lynne's sketchbook, which shows her working out how to illustrate this part of the story.
Notice in the bottom corner, the decision being made about which slippers Lynne will give Mum to wear: