Agreed Taftazani, sir. The first three books I would recommend for 9-12. Books 4-5 I suggest for 12-13. As for 6-7 I suggest 14-16 year olds.
Lord of the Rings and the Hobbit by JRR Tolkien are a must. Some books of CS Lewis like Chronicles of Narnia as well. Shaykh Asrar Rashid likes a lot of books by Roald Dahl. (Dahl was one of the few Western voices to criticize Salman Rushdie) With parental guidance, the Harry Potter books are also good for young adults. From the Greek classics there are a lot of good stories. We have our own fictional stories too in Arabic/Farsi etc.
"Fing" by David Walliams is a pretty humorous work for younger readers. But avoid the same author's "Boy in the dress" (the clue's in the name)
As-Salāmu Alaykum I would recommend the Lord of the rings and the hobbit by Tolkien. Also the septimus heap series by Angie Sage is good.