Allan Ahlberg 
Funnybones: The Pet Shop [EPUB ebook] 

In a dark dark street There is a dark dark house . . .In this FUNNYBONES story, the big skeleton and the little skeleton are fed up with the dog skeleton and decide to swap him at the pet shop. They start off with a goldfish but soon get tired of him and swap him for a parrot — but soon they get bored of him too . . . Eventually the pet shop owner gives them a box to take home with a surprise pet inside. What do you think it will be?