I'd forgotten about that one, Daffodil! George's Secret Key to the Universe - Stephen and Lucy Hawking- was one of the first novels my son liked! The perfect novel for a kid who loves space and science.
Also, what about James and the Giant Peach, Charlie and the Chocolate Factory etc.
My son enjoyed the Ramona books by Beverly Cleary when he was about that age,
Look at Farley Mowat, maybe, if he is outdoorsy.
We also liked Lynne Reid Banks-- all her books,...