Owly, Babymouse, the various books-turned-GN stuff (Nancy Drew, Hardy Boys, Boxcar Children), Sam and Alex, Jellaby...there are so many good GNs for kids! Warriors also has a GN series now (it's cats, but I guess there is kind of fighting that goes on). There's a cute series called Knights of the Lunch Table too.
For those that don't mind something a little scary or with some fighting, I love Lions, Tigers, and Bears. Beautiful, beautiful art. I would say that's more for older kids though. Amelia Rules is good for slightly older kids too.
GN stuff for kids is hot! I help manage/put together the GN section of our elementary school library, so I've been up to my elbows in it!