Children are hardly cruel. Selfish and self-centered, perhaps, but not cruel. Cruelty implies some sense of malice and contempt--perhaps even a hint of sadism--but children do not yearn to hurt or harm others, to see them in pain and agony; they merely want their immediate desires to be fulfilled. For a child, the end always justifies the means, and it is that need for instant gratification which may be deemed cruel by an outside, adult observer.

As a side note, please keep in mind that innocence does not, in any manner, have the same meaning as kindness. Innocence is merely a nicer word for ignorance, and until a child has been taught the rules of society, he or she cannot make a decision as to whether or not willingly break or uphold them. The malice usually associated with cruelty is difficult to form without the knowledge of society's structured set of rules and regulations, which, of course, comes only with the loss of innocence.