Who is Patla Babu and Jhaaria Babu from Swimming Lessons and what is their importance?

In "The Collectors," Patla Babu and Jhaaria Babu are street people who set up daily on the pavement outside St. Xavier's Boys School and do a brisk business selling items of interest to schoolboys. Their real names unknown, they go by the descriptive nicknames for fat and skinny. The beggars stoically endure theft, but when it involves costly stamps, they turn in the head "flicker," Eric D'Souza, and stamp collector Jehangir Bulsara to school authorities.