Agreed, but again this has to be taken into context, The Hobbit was a children's story, and LotR was originally its follow-up that developed into its own.
Today, I would classify LotR as as Young Adult novel and not an adult piece of fiction. Honestly, it's themes were vastly mature compared to the Hobbit, however they weren't exceptionally mature for the time it was written. Consider that Return of the King came out in the same year as Lolita, and Fellowship/Two Towers came out in the same year as Lord of the Flies, which is another 'adult' novel that is arguably a Young Adult novel, although IMO deals with a much more mature subject.
Hobbits are a long lived race. Frodo had only recently 'came of age' when the story begins, IIRC at 33 years old. Considering the traditional ages of 'coming of age' I'd bet he was the maturity equivalent of ~15 years old, and he certainly behaves like it in the beginning.
IMO LotR was a great YA novel, just like The Hobbit was a great children's novel. They're amazing stories that you can sit down and read with you kids, but you're not necessarily going to be enjoying them as much as they are, and in 20-30 years time, your kids might be reading them to your grand kids and feeling the exact same way.