Is the book Lord of the Rings suitable for a 7 year old?

I would recommend the Chronicles of Prydain by children's author Lloyd Alexander. It is a 5 book series in the fantasy genre and the final book won the newberry medal in 1969. I read this series when I was in the 4th grade and again when I was in the 7th. It is a wonderful story loosely based on nordic mythology. The LOTR is wonderful and if your question is more directed in "appopropriate content" for children, I would say yes in that light just as the movies were very clean.

Note that it isn't really a trilogy, it is six books and six appendices published in three volumes.

Depends upon what age you are talking about. For the most part I would say for teenagers and above it is great.

For younger ages I believe it is too slow and too big a read to be truly appreciated by most of them, but there are some 11 and 12 year olds that might enjoy it. It might be better to start them off with The Hobbit.

Definitely start with The Hobbit. Easier language and less of a dark mood. However, after that, The Lord of the Rings is a great book.