While perhaps "innocent" isn't the proper word, there are certainly people who are sweet-tempered, good-hearted and altruistic, they tend to see and expect the best in others. In that sense they might be a touch "naive," although in some cases their high opinion of their fellow humans may be based primarily on faith in human nature rather than all of their real-world experience. (Elwood P. Dowd, the character played by Jimmy Stewart in the motion picture "Harvey," is an extreme adult version of this type, although of course his best friend is an invisible [to most other people] anthropomorphic white rabbit over six feet tall.)
I've come across children like this, some of them relatives but most of them young campers at a Christian summer camp I worked at for over a decade, so I know they do exist, preteen kids who are good-natured, caring and considerate. Of course, there are also children who are devilishly full of mischief, tricky and even manipulative (fictionalized versions of them often work well as characters in spanking-oriented stories), then there are some who are truly antisocial and behave negatively, possibly even violently.
I'm hardly claiming that anyone should be trusting of a young kid merely because he/she is a child, but automatically assuming negative things about him/her isn't justified either...

--C.K.