The US K-4 Visa allows the children of a Thai spouse and a US citizen to come with their parents to the United States. This type of visa is only available to those Thai parents who have successfully applied for a US K-3 Visa or US Spouse Visa. The US K-4 Visa is valid.
The US K-2 Visa in Thailand allows children of a K1 Fiancée Visa holder to enter the United States while waiting for an immigrant visa to be available for them. To be eligible for this type of visa, the applicant should be an unmarried child of the K1 Visa applicant holder and should be.