A Children's Poem?

After hearing The Highwayman in class, I decided to do some research on it.  It doesn't really seem like a children's poem, but I really enjoyed it.  I found that highwaymen, or horsed thieves, were common in England between 1650 and 1800.  They gained respect due to their gentleman-like attitude.  They also always well dressed, which is made evident in the poem.  It was published by Alfred Noyes in 1906 and gained instant success.  Noyes was only a young man.  He is also know for writing The Barrel Organ and several other collections of poetry.  

Personally, I loved the poem, as well as the version put to music we listened to in class.  The vivid descriptions and great story make the poem worth reading over and over again.  However, I still do not understand how a poem of this nature can be considered children's literature.