It has a Lexile score of 1000. Don't expect the English to be EASY. I think it is intended to be read TO children, not to be read BY children.
It uses good grammar, good English usage, good writing style, good vocabulary, and is free from colloquialisms and slang, so it is a good book "for learning English." The general tone of voice is soft--like a fairy tale, not like an action thriller.
If you tackle it, be ready to come back here with more questions.
Here's a long, relatively difficult sentence from the book:
"'All the same, I should like it all plain and clear," said he obstinately, putting on his business manner (usually reserved for people who tried to borrow money off him), and doing his best to appear wise and prudent and professional and live up to Gandalf's recommendation."
Here's a relatively easy one--still long, though:
"'There they mined and they tunnelled and they made huge halls and great workshops--and in addition I believe they found a good deal of gold and a great many jewels, too."