Kefir is cultured milk product and consumed in Eastern Europe and Russia. Have you seen a yogurt drink which has a tart taste in Turkish restaurant? It is compared with yogurt sometime but contains different types of beneficial bacteria than yogurt does. Kefir's bacteria can actually colonise the intestinal tract unlike yogurt, and also contains beneficial yeast too, which helps control and eliminate destructive yeast in the body. It sounds like kefir is quite superior than yogurt as a probiotic food.
In the baby cooking book that I was reading, we only need small amount such as 1 teaspoon mixed with soaking water for 100g of wholegrain that make wholegrain more digestible for baby's digestive system.
If anyone have a gentle tummy, it is worth adding kefir in the soaking water for wholegrain and legumes/ pulses (as well as drinking).