Which type of visa for child who currently lives with us in China, and is turning 18?

I cannot find any conclusive and certain information for the following situation. Any help is greatly appreciated. We have resided in China for a year and have our Residence Permit for Foreigners. Our son is currently 17, lives in China with us, and is soon graduating from high school. He will turn 18 and wishes to continue to reside in China with us after he turns 18. He will eventually attend college in China, but it might not be until September of 2015. In order for him to be able to remain in China with us, which type should he have to cover the time span in between turning 18 and attending college? Thank you.