It doesn’t have to be a newsworthy event or a public figure for the photo to be legal, whether it’s for publication or not, as long as the photo is taken in a public place under normal circumstances.
A few things can complicate this, however: one, if the photo puts the person in a “false light,” whether through the subjective nature of the photograph or an inappropriate caption, the photographer and publication can be successfully sued for libel.
Secondly, a minor’s privacy is generally more protected than that of adults; most if not all professional photographers get releases for minors even if they don’t for all their subjects.
Thirdly, several states have recently passed laws making secretive phototaking for the purposes of “sexual gratification” illegal. This covers the guys taking photos of kids on the beach and people with mini digital cameras taking photos up girls’ skirts.