Mvt 1 "Happy Times" is pretty self explanatory. It's child-like sound is what defines this movement. 
Mvt 2 "Scherzo" Taking fragments of Liszt's "Mephisto Waltz No. 1" and Ravel's "Concerto for Left Hand" along with a variation of the 1st movement theme is the basis for this movement. It continues only to fade away from a false sense of reclaiming the moment of happiness.
Mvt 3 "Song of Blue" This movement is the basis for the "Blue" title. It is the story of two people who while they care for one another eventually must go their separate ways due to life and fate.
Mvt 4 "The Hammer" Imagine a child striking an object with two hammers. My mother apparently has a picture of me doing such a thing though I have yet to see it. Eventually like all things, playtime must come to an end.