Explain themes of Childhoods joy and Innocence in Dylan Thomas "Fern Hill"

Fern Hill is a lyrical poem filled with metaphor and rich language depicting the simple joy of a child playing outside at one with the spirit of nature and the grace of childhood.

And nightly under the simple stars
As I rode to sleep the owls were bearing the farm away,
All the moon long I heard, blessed among stables, the nightjars
Flying with the ricks, and the horses
Flashing into the dark.

There is an innocence throughout the poem that readers might have one experienced but lost as maturity inevitably destroys the magic.