The rhyme is a genre of folklore that originated a long time ago. It now rhymes are views of children's creativity, as in ancient times, surprisingly, rhymes used by adults! They used rhymes to spread the work, for example, the role before the hunt. Because many types of work, especially back then, were very difficult, sometimes dangerous to health and even to life. Few people voluntarily want to take on such work. And rhymes were allowed to distribute the work between the participants so that no one was hurt because the heavy work was not sent because you can not argue or don't like the main, and because it fell on the account, that is, after all, justice (read, what were the rhymes in those days).
In our time, this role rhymes already lost, but they still perform the function of roles, not only in the work and in games.
And a few words about why the rhymes are often used strange, non-existent words. It also goes back to ancient times. In those days, people strongly believed in the power of words, rhyme was something similar to a spell. Rhymes were often used for divination. And even at that time people were not yet able to explain many phenomena of nature, and therefore was afraid of her and spiritualized. For example, people believed that animals understand human speech. So, if you are going to hunt, they tried not to use common words and replace them with "secret", secret: suddenly the beast will hear what they say, and understand that they are going to hunt for it.
Now it is often difficult to determine what rhymes come to us from antiquity, and which appeared recently: this genre has not at all and has not lost its relevance, and new rhymes. They continue to help children rapidest role in the game so that everyone had fun and no one is hurt.