The terrible tedium of Arrietty's life before she meets the Boy is shown rather comically, I felt, in her excitement at washing day when she can go and hang the washing out by the grating. Her mother Homily in the film is more comical and loveable than the fretful, nagging and fearful character she is in the book. Arrietty's shock at the discovery that, instead of the rare creatures she assumes, "human beans" are in fact numerous and Borrowers are rare is shown in a powerful and affecting moment of stillness.
A big difference (and this is inevitable) is the lack of the framing device of the old woman narrating the tale to the little girl, and an unreliable narrator telling us about that: we are told very firmly that the little girl is not the "me" sitting and listening to the story, and this emphasises the uncertainty at the end of the book, when Mrs May isn't certain that her brother hasn't been making up the story all along (we're told he is very imaginative), since the handwriting in Arrietty's Book of Memoranda is so similar to his.
Michelle Harrison's The Thirteen Treasures reminds me strongly of The Borrowers, although the relationship between fairies and Tanya is not the generally benignly symbiotic one between the Clock family and the Human Beans; these fairies are malevolent, jealous and threatening. Like the Boy in The Borrowers, Tanya is sent to live with an elderly relative (this time her distant and seemingly unloving grandmother) in a remote country house. Tanya has a secret: she can see fairies. And they can see her. They torment and threaten her, and she is blamed for the damage they do to her possessions and house. Her mother can't cope any longer, so she is taken to live with her grandmother in Elvesden House in Essex. However, there is also a secret connected to this house, involving the mysterious disappearance of a young girl many years before, and if Tanya and Fabian, the caretaker's son, don't solve the mystery, there is a danger that history may repeat itself.
I would recommend the film to 6 year olds+; it isn't scary, but it may not hold the attention of younger children. I would suggest reading The Borrowers to 7+. It isn't a long book by modern standards but the narrative is quite complex; advanced readers 8+ should love reading it themselves. The Thirteen Treasures is a fantastic book for confident readers of 9+.