Katniss and Peeta lived happily ever after together with their two children. But they died of disease. So their children went as orphans and got adopted by the Priors.
They changed the children's names to Beactice and Caleb. When they both turned 16 they chose other fractions. Beactice chose Duntness and Caleb chose Eunite. Beactice changed her name to Tris and lived a happy life with Tobias.