I have seen the Disney film "The Three Lives of Thomasina" several times, but never read the book before now. I will say right off the bat that the movie follows the book very well.
Thomasina is the much-loved cat of a little Scottish girl named Mary Ruadh MacDhui. Her widowed father is the town veterinarian, and he is one angry guy. When Thomasina falls ill, he orders the cat euthanized. Mary and her little friends have a funeral for the kitty ... who is found by "Daft Lori," the woman who helps all of the local animals with which the vet will not be bothered.
Part of the book is told in the first person from Thomasina's perspective. It is an utterly charming book. I would say that reading it with very young children might be difficult, as there are a lot of sensitive parts. However, those 10 and up are likely to be charmed by Thomasina and her friends.