Malorie Bantala, 21, was 32-weeks pregnant when she was assaulted by two people in Peckham on 15 June.
A boy, 17, was charged on Tuesday with child destruction and grievous bodily harm. He is due to appear at Barkingside Magistrates' Court later.
Kevin Wilson, 20, was charged in June with child destruction and causing grievous bodily harm with intent.
The teaching assistant, of Longfield Estate in Bermondsey, who is believed to be the baby's father, denies the charge and will face a trial in November.
A second person has been charged over an attack on a pregnant woman in south London after which she lost her baby.