Visa or travel documents for my kids

Dear Sir or Madam,

We would like to take our children to visit their beloved grandparents and China this summer. Both my wife and I are holding Chinese passports. Our two kids were born in US (now, 11 and 7 years old) before we obtained green cards. They both got travel documents before. Based on the information that we gained from the website, we reason that we should apply for travel documents for my kids again, since theirs were expired. Please advise!