Yes, they're suitable. My 9 year old is ploughing through them and I'm reading them to my 7 seven year old. I'll probably read another couple to the 7 year old and he'll be off on his own after that. I've read Little Foxes, Born to Run, Kaspar and King of the cloud forests and they're very good. I challenge you to read them without getting a lump in your throat at the end. Just about to buy some more.
Michael Morpurgo does books for every age from new readers onwards but the difficulty is finding which ones are suitable at which age. He never patronises or shires away from difficult subjects and for that reason it is important to know which are right at a given age. His wesbsite doesnt help a lot with this unfortunately. I have read Cool and Not Bad for a bad Lad, Black Queen over the past two years with my son who is 8. One of the best childrens writers but hard to tell which order to read them in!