The film concentrates too much on the mothers reaction to the situation, and the producer of this film ruined it by not telling the proper story on film, as the ending couldn't be more different from the book. DON'T buy the film version of this book, its not authentic.
The only difference is the cover. The movie tie-in edition has a picture of the actors on the cover. That's all - there's no difference in the text. Mrs I A M Roberts seems to think the movie tie-in book is a novelisation of the film - but it isn't! It's the same book with a new cover, that's all.