There is ongoing investigation in this area on mother-child transfers of gut bacteria that may influence body weight. The evidence seems to be pointing to diet

There is ongoing investigation in this area on mother-child transfers of gut bacteria that may influence body weight. The evidence seems to be pointing to diet influencing the type of bacteria that thrive in the gut - so my gut (ha ha) says that a few bacteria entering the gut won’t change things - you need to more or less farm them.