Children are not less intelligent than adults; what they are is less informed.
There's a hunger for stories in all of us, adults too. We need stories so much that we're even willing to read bad books to get them, if the good books won't supply them.
The Lord of the Rings' is fundamentally an infantile work. Tolkien is not interested in the way grownup, adult human beings interact with each other. He's interested in maps and plans and languages and codes.