K-3 Spouses of US Citizens and K-4 children of K-3 Visa Holder
K-3 visas are issued to spouses of US Citizens, whether the foreign national spouse wishes to immigrate to the US or not. It is a good mechanism for bringing a foreign spouse to the US while they await for an immigration visa.
Please read Marriage To A US Citizen
K-4 visas are issued to the unmarried children of the K-3 visa holder, so long as they are under the age of 21.