We emailed the Manila embassy that we would like to process the K2 children follow to join - In our case, the case needed to be transferred from HK to the Philippines. Once transferred, we received an email back from the embassy about the process, 1) we filled out the DS160, 2) paid their visa fees, 3) scheduled their embassy interview, 4) schedule their medical exam, and 5) They attended their interview. This took several flights and hotel stays back and forth between their home town and Manila. Their ages were 10 and 15. We had them memorize facts and details about me, my address, my work, etc for the interview. There were a few questions that they asked the kids and they did very well. My wife flew to the Philippines from the US for the embassy interview in March and I flew out to the Philippines in May. We picked up their passports with the k2 visas in May after I arrived. We all flew back together at the end of May. No problems departing the Philippines or arriving in the US (Chicago POE). We didn't have to deal with the father's allowing the children to leave because they were out of the picture and the Philippines law assumes the mother has full custody, I guess. All I know is that it went as smoothly as it could given the level of complexity that the immigration process entails. We were very blessed because I've read other horror stories on VJ.
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1) DS160-We filled out 1 DS160 for each child and saved / printed the DS-160 confirmation page.
2) Paid visa fees - Paid the fees locally and obtained a receipt
3) Scheduled their interview - We used the receipt number to record the payment on the ustraveldocs website for the Philippines which allowed us to schedule our interview
4) Scheduled their medical exam - We needed to have the the interview letter to schedule their medical exam. The medical exam required lots of paperwork (Interview letter, immunization records, passports, passport sized photos, DS-160 confirmation page)
5) Attended their interview - We took the (medical exam results, original petition, i-134, interview letter, ds-160, passports, passport sized photos, marriage certificate, petitioner divorce decree)
The kids are in the US now and are adjusting to the new culture, schools,etc. They love their schools and are getting English language assistance now.