In addition to what Phil said, since children don't know the "rules," they innocently and easily break them, allowing their natural creativity to flow. As adults, we become steeped in rules, and it often stifles us. For instance, there's a rule about not putting the subject dead center, but there are occasions when the beauty of a photo is brought out only by breaking this rule.
Of course, it helps to first learn the rules and understand them. Once we do that, we should all feel free to break them. The worst thing that can happen is a bad photo. (I have a huge collection of these.