Caroline is a top contender if this DC is a girl but we need a nn (we tend to use a mix of full and nn with our other DC.
We cant use Cally as already in use by a family pet (!) and I'm not a big fan of Carrie really. I came up with Cara as quite often Caroline sounds more like 'Caraline' when said out loud - is this too much of a leap?
Any other nn suggestions? Must begin with C! (I have this thing about nn starting with the same letter as the full name)