谢8老师！再多问一句：孩子双亲写的信（委托书），中文，让中领馆公证，认证，就可以出中国海关吧？
-孩子双亲写的信 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 中领馆公证，认证 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 旅行证 is void, you had better contact the local 市或县公安部门 (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.
