謝8老師！再多問一句：孩子雙親寫的信（委托書），中文，讓中領館公證，認證，就可以出中國海關吧？
-孩子雙親寫的信 or consent form is used for entering US if the grandparent accompanies the child. See the following links:
See these links for the sample letter or consent form (you may revise it for your case):
You don't need to do 中領館公證，認證 and just go to the Notary Public (e.g. your Bank) to notarize your signature on your letter (see above link).
Because your kid's 旅行證 is void, you had better contact the local 市或縣公安部門 (即出入境管理局）who deal with the departure out of China. They will help you out. It should be easy.
By the way, your kid travel back to US is irrelevant to teh Chinese Embassy in US, so don't bother them.
