I keep a guitar around while writing and will improvise music. I do this for several reasons, such as that it's fun, and sometimes it helps me with the meter.
Frankly, writing poetry for children is plain old fun, and I consider myself blessed to have such a delightful career.
I invented animals and birds - I had about two dozen. After working on them for six months, I sat down and just for fun wrote two dozen poems to accompany the drawings. It was for no one to every see, but a friend sent me in to an editor.