I am sorry I did not pay attenton to that you are a US citizen in my above responses. Because you are a US citizen and China have joined Hague Adoption Convention, the 2-year joint residence and legal custody by residing with the child must be completed in China, not in US, and that means you need to go to China to live with the child if you want to use family petition adoption process. The 2-year residence with the child does not have to be continuously and may be counted in the aggregate. So, you can adopt the child and get the formal grant of custody from a court or other government entity in China before the child turns 16th birthday, and complete the custody and 2-year residence requirements and file I-130 petition for the child immigration application before the child turns 21th birthday.
The 2-year legal custody and joint residence requirements are waived for certain abused children. So, if you can prove that the child is abused in the original family, you may get two-year joint residence requirement waiver. Then, adopt the child in China following the Chinese Adoption Law and file I-130 petition for the child immigrant visa application to US immediately after the adoption is completed.
