So, these "the little ones", who are they?

The concept of probiotics was first introduced in the 20th century by Noble prize winner, Elie Metchnikoff (1845-1916). 

He himself introduced in his diet sour milk fermented with bacteria he called “Bulgarian Bacillus”, later called as “Lactobacillus delbrueckii subsp.” and found his health benefited. The root of the word ‘ probiotic’ comes from the Greek word pro, meaning “promoting” and biotic, meaning “life”.