Yes, China cares about NK, as do the US, SK, Japan, Britain, France and any other country that has enough time to care about international issues...
There is no doubt. North Korea is notoriously crazy stupid. Kim Jong Il was a badass and a half, at least in his own mind. They pushed the boundaries for a long time but we kept them in check. However, we currently have a president, Obama, that is weak on military prowess. If that's not bad enough, Kim Jong Il died giving way to Kim Jong Un who feels he has to prove himself as a greater leader (or god) than his father. This combination has led to over confidence and a narcissistic psychopath bent on showing the west we need to fear him. They have done nothing but work on nuclear weaponization and ICBM research and development. In the recent past, with Kim Jong Il, China and NK had an agreement, now, even china doesn't trust that nut bag. My guess is that's one of the reasons for China's expansion into the Pacific. They see Obama is weak and won't protect our allies, Japan doesn't have a military because of our WWII agreement, who else is out there with the military power to deuce on NK hard and fast if they do something really stupid?
It cares about virtually all of its neighbors, to some extent.
I was always of the impression that China was just using NK as a buffer zone between them and staunch US ally SK. Though in recent decades China has been developing a closer relationship to the West, so NK is starting to become inconvenient (and a little annoying).
No country cares about each other - you cannot trust anyone nowadays.