China visa for minors

I am taking high school students to China. All are under 18 and we will be using the Chinese Embassy in Chicago to get the visa. Do we need copies of the students' birth certificates, copies of their parents' passports, and/or an authorization letter or form from parents stating they give permission for their children to travel with another adult? Please let me know if all or none of the above are required. If we do need a parent authorization letter or form, is there a specific form required or should I draft my own letter? Thank you for any assistance you can provide.