Kimberly is okay, but I wouldn't use it even if I didn't already have a cousin named
Kimberly. I know that o the charts it's popular but offhand I can't think of a very young
Kimberly. I think the youngest I know is a teenager.
I don't know any
Kimberly that regularly goes by the full name, they all seem to go by
Kim. The fact that
Kim seems to be the inevitable nn for
Kimberly shouldn't necessarily stop you from using it, after all, you can call her
Kimberly till the cows come home. It might stick with others.
But try as you might, she may decide later on that she prefers to be called
Kim, and by that time it's really out of your hands.