more details for the visa

1. They have good financial situation. they have at least 1-2 M(RMB) deposit. but We though too much may hurt it. So They got a deposit documents with 300,000 RMB
2. We are sponsors for his trip (we first though to visit both the boy and his Mom, then think one F1 for Boy and B1 for his Mom will make it complicated, so just the boy this time).
3. We found a school in Boston which has summer program for children and can provide I-20 (they must be authorized by some agent).
4. Support documents from us: passport of both of us, salary stub, bank statement, our legal status documents(AOS). original application for his program.
5. Their documents: deposit, letter from school said he will continue next semester. Salary stub of both parents
6. Key points for succeed:
a. good financial records.
b. He has NO intention to stay here for middle school (they ask details of his current study and future plan).
c. both family have one kid, so NO intention for adoption, we also bring lots of pictures of two families(they ask the boy many details of our son), Since our son (6 yrs) stayed in China for one year and they are very familar with each other), so he is very confident in answing those questions.
d. Both are happy family, no divoice(they particularly ask this question)
7. His mother company him for interview. But they ask the boys most of questions(I guess kid tend to tell the truth), such as how he will come here since only he applied for visa. ( we will visit China and bring here, leave our son in China for 1-2 month, they send him back when one of us back to China to bring our son back), where he will stay while in USA. Actually the first question is will he bring Camera to USA (he answered 'NO' since there will be lots of here, why ask this ?), ask occupation/salary of his parents, our salary, other family members.