'Miracles' shows and appreciation for all things in life. Whether large or small or such and such. Basically Whitman is showing a great deal of love for all things living, dead, or inanimate. He appreciates other people, animals, little things like just seeing a bird fly bye. He seems to be high on life.
I'm not sure exactly what this poem means, but i think it has something to do with THE creation. Or creation as an artistic subject, something to that affect anyway. I think the lines starting with 'what do you suppose creation is? ' are saying that our souls will only be satisfied if we are equal with God, and feel some kind of freedom from him.
Walt Whitman is basically trying to say that the world isn't perfect. And that it isn't safe for kids to perceive it that way, let alone grown men and women. I like this poem and appreciate its meaning.