The casualties occurred on Saturday night in New Usmanpur area in east Delhi. The firefighters took an hour to douse the blaze that broke out around 11.30 p.m.
"At least 25 shanties were gutted. The fire possibly broke out due to an electrical short circuit. We sent 12 fire tenders that doused the flames by 12.30 a.m. on Sunday," said a DFS official.
The official said the firefighters found the burnt bodied of Reena, 10, Meena, 7, and six-month-old Mubarak from one of the gutted shanties.
"One child with over 80 percent burn injuries was battling for life in a city hospital," he said.