I read just about every piece of Sci-Fi he wrote, all of the robot series and indeed I bought book when I encountered it many years ago. As a teenager he was top of my list.
One of my all time favourite Sci-Fi authors and of course, his Three Laws of Robotics are now canon for almost ANY robot story.
This was indeed written as a children's book. The (to me) really interesting information about TLOTR is that Tolkien, being a philologist was inventing a language but felt the need for the language to have (for want of a better term) a 'back story'. To be real, he had to invent a race to use the language - and hit on the concept of using Elves.
He then wrote TLOTR as well as a whole host of other shorter myths and legends of his Elvish race which his son Christopher eventually collected, edited and finally published as The Silmarillion.