Police apprehended the 14-year-old juvenile after the victim's family registered a case against him.
The incident took place yesterday afternoon at the victim's residence in Rangpuri Pahadi slum cluster.
"The girl was playing with the boy in a room when the boy allegedly inserted a pencil in her private part. As the girl started crying, the girl's mother took her to a Safdarjung Hospital where medical examination revealed that she was sexually assaulted," a police official said.
Police registered a case under the Indian Penal Code section 376 (punishment for sexual assault) of the Criminal Law (Amendment) Ordinance, 2013, and section 6 (punishment for aggravated penetrative sexual assault) of the Protection of Children from Sexual Offences (POCSO) Act and apprehended the juvenile from Rangpuri Pahadi area.