כפרות

DAF HASHAVUA (Shabbos 81b) part # 1 Rashi quotes from the Teshuvas Hagaonim.  “Twenty-two days or fifteen days before Rosh Hashana a bean was planted for every child in the house in a   flower pot.  On Erev Rosh Hashana they swung the new plant over the head of the child and said זה חליפתי etc. Afterward the plant gets thrown into the river". The Magen Avraham (O. Ch 605) writes that this Rashi  (Teshuvas Hageonim) is the original מקור (source) for כפרות as we know it today. The question arises why do we do כפרות  for Children and even for the unborn?  Children before reaching the age of Chinuch have absolutely no obligation to do Mitzvos. The unborn definitely have no obligation to perform Mitzvohs in the mother's womb. A pregnant woman is not required to drink an additional 4 cups at the Seder for the fetus in her. So why is כפרות different? Perhaps we can answer. We do Mitzvos and Minhagim, because The Torah or Chazal commanded us to do so. Some Mitzvos come along with their Segula, (למען יאריכון ימיך) but the primary reason for doing it is not for the Segula but because the Torah commanded us to do so. The Minhag of כפרות is different, the sole purpose to do it is for the Segula to save the children from dying. We also want and need protection for the unborn as well. Therefore we do כפרות for children and the unborn. The original Minhag of כפרות was solely for the protection of the children. Eventually, adults also adopted the Minhag אמבצי