Children's books can't be fitted into rigid age categories. There is always overlap with younger and older children, and the better the book the greater the range. The ages suggested here are intended to give a rough idea of the range for which a book is likely to be appropriate. Books in the "3 to 7" range can be read aloud to younger children; older children may be able to read them on their own.
A Wizard of Earthsea, by Ursula Le Guin. A breathtaking story, not to be missed by avid readers aged about nine upwards to adult. Described as "one of the greatest creations in all of fantasy literature", this is the first book of Earthsea. Those who love it will want the others in the series too, The Tombs of Atuan and The Farthest Shore; and will re-read them to pieces. There was a fourth one, Tehanu, which came out about twenty years after the first three and which I haven't read. Earthsea fans I've spoken to were disappointed in it. Ursula Le Guin has also published several highly acclaimed books for adults. (Click on the titles to read more on Amazon).
The Wheel on the School, by Meindert de Jong. A substantial novel for avid readers aged about nine upwards. Set in Holland and peopled with memorable characters, it's a beautifully-told story about six children trying to entice storks to return to their village at nesting time. It won the Newbery Medal many years ago when it first came out. Trophy Press, US$4.50. (Click on the title to see more on Amazon).
Babe, The Gallant Pig by Dick King-Smith. I believe this was originally published in England as "The Sheep-Pig". Those who read the book are unanimous in preferring it to the movie (which I haven't seen). The book is great and Dick King-Smith is a good writer to know about for children aged about seven to twelve who want and need something of substance to read on their own. It has character and humour and a good story, believable while you are reading it despite the unlikely premise. Knopf, 118 pages, US$4.99. (Click on the title to see more on Amazon).
Revolting Rhymes by Roald Dahl (Puffin). High comedy for kids in Roald Dahl's rollicking parodies of six traditional fairytales. Full colour. Any age from about 8 up. A slim paperback (49 pages), US$4.99. (Click on the title to see more on Amazon).