This is the US K-2 Visa application process. If you are an American citizen who plans on marrying your Thai fiancée in the United States, and she has children that she wants to bring with her, then the US K-2 Visa is the most appropriate type of visa for your case
US K-2 Visa Application
A US K-2 visa allows the Thai fiancée of a US national to bring their child or children with them to the United States and get married. The Thai fiancée’s children can apply for the US K-2 visa at the same time as your fiancée is processing her US K-1 visa, wherein they will receive their US K-2 visas when your fiancée receives hers.
Successful US K-2 visa applicants may travel to the United States with their parents or follow them later on, and holders of this type of visa are given one year to enter the United States from the date the US K-1 visa was issued to their parents. US K-2 visa holders should apply for a green card within 90 days from their arrival.
Children and other minors
Only those children who are below 21 years old. This and are unmarried will be eligible to apply for the US K-2 visa. Those children who have been barred from entering the United States. This due to immigration violations before will not be receiving a US K-2 visa.
When your Thai fiancée wishes to bring the children with her to the United States, you should apply for their US K-2 visa simultaneously with your fiancée’s US K-1 visa application. See to it that the children’s names are listed on the I-129F form. That you have for your fiancée’s US K-1 visa application. When the children’s names are in the petition that you filed. There will be no need to file a separate petition for them. You will be receiving an instruction packet once the I-129F petition. This makes it through the system and reaches the US Embassy in Bangkok. This instruction packet will give you an outline of which documents and forms are needed and should be gathered in order to obtain the US K-1 and K-2 visas in Thailand.
K1 Visa Process
Once you have received the K visa instruction packet from the US Embassy. You should then start to gather all the needed documents, as well as fill out the proper forms. The fastest method in completing a K visa application. Is by gathering all the required documents for your fiancée and US K-2 documents for the children altogether. Separate forms are required for each applicant. This so it is necessary to follow instructions and see to it that a complete set of forms. These are submitted for all the applicants of the K visa. Also, everyone applying for the US K-1 visa is required to submit their birth certificates. For those without birth certificates, you can either use school, hospital or baptismal records instead. All the applicants are also required to have valid passports and passport sized photos.
Your Thai fiancée should be able to show proof. That she has permanent custody of any minor children when applying for K visas. If a child is born from your previous marriage, a divorce decree stating that she has full custody of the children would satisfy this requirement, or any official statement from a Thai court or local Amphur granting your Thai fiancée permanent custody and consent to permanently move the child to the United States. A different certificate should be obtained for those children who are born outside of your Thai fiancée’s previous marriage. However, for older children (16 years or older), you will be required to obtain a certificate from the police showing that the child has no criminal record. This can be done at the same time when you obtain a police clearance certificate for your Thai fiancée.