To understand their Chinese side of background; to be able to assimilate themselves with their families and their Chinese friends (here or friends they make in China, if they travel to China), to appreciate good things in Chinese culture (in the long run).
Because it is not their daily language, I won’t expect them to recognize a lot of Chinese characters, not even to write that much. As long as they got enough exposures, it will benefit them and us in the long run. We will be able to communicate better.