The following specific recipe comes from Super Nutrition for Babies by Katherine Erlich and Kelly Genzlinger:
Fermented cabbage is extremely nutrient rich, a half cup (71g) offering 30% of the daily value of Vitamin C in just six calories. Additional lactic acid, enzymes, and probiotics make this food a perfect digestive aid. Sauerkraut and sauerkraut juice are remarkable at stimulating adequate stomach acidity, which makes them protective against food allergies.
4 cups (360g) finely chopped or grated loosely packed cabbage
2 tablespoons (28 mL) whey or culture starter
2 teaspoons Celtic sea salt
Mix the ingredients and then tamp down in a quart-size mason jar.
Fill with water (about 1 cup [235 mL]), leaving at least 1 inch (2.5 cm) to top of the jar.
Seal and allow to remain at room temperature for 3 days; then move to refrigerator storage.
Alternatively, buy unpasteurized sauerkraut, such as Bubbies brand, at the health food store.
Instead of whey, you can use culture starter
You can spoon 1/4 teaspoon of the sauerkraut juice to your baby before cooked meals
If you’re nursing, eating sauerkraut with your meals will help improve your digestion, resulting in less heartburn, more nourishment, and fewer immune responses to foods for both you and your baby
You can finely cut-up bites of sauerkraut to your baby at 10-12 months