A beautiful introduction to Middle Earth. It is much cosier than the Lord of the Rings, with a scattering of rhymes to jolly it along.
In some ways it's a simple quest narrative, but already you get a taste for the breadth and depth of Tolkien's imagining of Middle Earth.
Although LotR stands on its own, it makes far more sense to read this first, though a child who enjoys it is not necessarily ready to tackle LotR on their own - not just because this is shorter and simpler, but also because it is a simpler kinder world it is describing.