Source of book: We own this.
Although I sometimes pick stuff to read to my youngest (the only non-teen, and also the only one who consistently wants to be read to), she often picks her books.
The Borrowers is one of my mom’s favorite books - she read it to us as kids. I never really got into it; I read the second book, but stopped after that. My kid liked it, though, so your mileage may vary.
The series was written by Mary Norton, an English author, in the 1950s, and seems a bit of its time and place. The house is based on one Norton lived in as a child, and the Britain of the book is very much the late colonialist Empire, before Indian independence. So, expect some casual classism and racism - not a lot, but just in the general attitudes toward India and servants.
The basic idea is that when items disappear from homes, what is really happening is that they are being “borrowed” by tiny hominoid creatures who call themselves Borrowers. These people seem very much like ordinary Englishmen, but on a much smaller scale. In the book, the three main Borrowers are Pod, the father, Homily, the mother, and 14-year-old Arrietty, who is coming of age in more ways than one.
The household is turned on its head by Arrietty’s discovery and befriending of The Boy, a 9-year-old who has been sent back to England (from Colonialist India) to recover from an illness. This contact is in turn driven by Arrietty’s dissatisfaction with her life. After all, they are now the only Borrowers left in the house, so she has no friends her age, just parents, and she never gets to leave their home under the floor.
The problem is, of course, that whenever a Borrower is “seen,” bad things happen. Humans do not react well to them, for the most part, and try to exterminate them - which is what happens in the book once the housekeeper discovers the Borrowers’ home. The boy is different, of course - children often are. He befriends Arrietty, but his carelessness in trying to make their lives better leads to their discovery, and the eventual need for them to leave the old house altogether and seek their fortune in the fields and forests.
Ultimately, the book is about that coming-of-age story. Arrietty must grow up and face the world one way or another. And the sheltered life her parents have made for her cannot last either. They are the last of their kind in the house - are they the last in the whole world? Besides, soon the last occupants of the house will be too old to continue living alone. What happens then? I suppose all of us facing change face that dilemma.
The original books were illustrated by Joe and Beth Krush, and are fairly distinctive. Along with these books, they are best known for Gone-away Lake by Elizabeth Enright, and one of the All-of-a-Kind Family books. So, not that well known these days.