good afternoon I'm engaged to an American. I have 2 children who are in Brazil. I would like to bring them to Ca the more people say that if they came and they will be considered illegal in the country I have the green card

You can apply for the greencard for both to come to ca.

To bring your children you need to petition the American Consulate, you need a clearance letter from the father, original and motorized translation of that document. Need birth certificates for both, original and translated. Before bringing them you will have to appear for a clearance hearing in Rio, after that you get the Brazilian consulate give you authorization passes with their Brazilian Passports. Boa Sorte/Good Luck