I personally wouldn't use Kelly (it feels kind of dated to me), but on a boy it does have a certain "hipster" charm to it. (I'd expect his sister to be Hazel.)
I don't know how many people on the BtN boards watch "Grimm," but the baby boy born this past season premier was named Kelly. In this case he was named after another *female* character, but I still think it fits well.
Please rate my personal short name lists (the latter includes combos):
www.behindthename.com/pnl/69381www.behindthename.com/pnl/69381/91835 (updated)
http://greens-end.myminicity.com