Potato dumplings are a guaranteed crowd-pleaser. Add apples to the cabbage to make it more pleasing for kids.
Cook the pierogi according to the package directions.
Meanwhile, heat the oil in a medium skillet over medium heat. Add the onion and cook, stirring occasionally, until tender, 5 to 6 minutes.
Add the apple, cabbage, parsley, vinegar, caraway seeds, ½ teaspoon salt, and ¼ teaspoon pepper.
Cook, stirring, until the cabbage is slightly wilted but still crunchy, 4 to 5 minutes. Serve with the pierogi and sour cream, if using.