MY PARENTS ARE BORN IN CHINA AND ARE US CITZEN NOW.

I'm afraid they cannot apply for it currently. If in the future they can satisfy the following requirements they may apply for the Chinese green card:
comes to live with a direct relative in China and has no other direct relatives overseas;
over 60 years old, has lived in China for five consecutive years, and shall live in China no less than nine months every year with financial guarantee for living and a residence.