WHETHER upon the garden seat
You lounge with your uplifted feet
Under the May's whole Heaven of blue;
Or whether on the sofa you,
No grown up person being by,
Do some soft corner occupy;
Take you this volume in your hands
And enter into other lands,
For lo! (as children feign) suppose
You, hunting in the garden rows,
Or in the lumbered attic, or
The cellar - a nail-studded door
And dark, descending stairway found
That led to kingdoms underground:
There standing, you should hear with ease
Strange birds a-singing, or the trees
Swing in big robber woods, or bells
On many fairy citadels:

There passing through (a step or so -
Neither mamma nor nurse need know!)
From your nice nurseries you would pass,
Like Alice through the Looking-Glass
Or Gerda following Little Ray,
To wondrous countries far away.
Well, and just so this volume can
Transport each little maid or man
Presto from where they live away
Where other children used to play.
As from the house your mother sees
You playing round the garden trees,
So you may see if you but look
Through the windows of this book
Another child far, far away
And in another garden play.
But do not think you can at all,
By knocking on the window, call
That child to hear you. He intent
Is still on his play-business bent.
He does not hear, he will not look,
Nor yet be lured out of this book.
For long ago, the truth to say,
He has grown up and gone away;
And it is but a child of air
That lingers in the garden there.

Robert Louis Stevenson

http://www.poemhunter.com/poem/envoy-for-a-child-s-garden-of-verses/