Clarence - My Diary of a Very Unusual Hamster by P.J. Kruger

Eleven-year-old Sid gets some hamsters from his parents who feel that he may enjoy their company as well as a chance to learn about ‘responsibility’. Sid decides to keep a diary. Sid’s diary entries follow the observations he makes in his unsuccessful attempt to keep and raise the hamsters. One of the hamsters, Clarence, a rather big black and white one with a funny look in his eye, just seems to get bigger and bigger whilst the others seem to mysteriously disappear. Sid eventually discovers why.