Most illnesses start in the intestines and that was something that was known by academics thousands of years ago. They just didn’t have the technology to prove it, only by observation. Fermented foods were used to repair the health of the gut. It is similar today except we can do proper scientific analysis and alter the diet to address the deficit.
This is why when using antibiotics one takes probiotics for three months to restore the gut bacteria for optimal health care. Not being a doctor I don’t know what age treatment should commence for babies. Though I do feel both paediatric and natural therapists care combined may be helpful. Also when to start babies on solid food may make a difference too. When I was a baby, babies were on solid foods at three months old, but when my babies were born the rule was 6 months old. That may work on some babies but not all babies. I had to start my babies on solid food by 4 months old or there about because they were clearly not getting enough nutrients. My doctor advised me to mix a malt type product into the milk formula to help them but it only worked for so long and then I had to introduce baby food. That was a laugh and a half, the first mouthful and baby is like, what am I supposed to do with this mush.
Modern society uses a lot of processed foods and they may not be good for infants and children and they may cause allergies and intestinal issues. Since the 1980’ there has been a significant increase in childhood allergies and asthma. You really notice this when your children are starting preschool and kindergarten. I was stunned when my oldest was starting kindergarten when I saw how many children had health problems. I was not around children up until that point because I didn’t know anyone with children. So it was a big surprise. My oldest child was an asthmatic and then developed other autoimmune health problems.