The incident occurred in Aman Vihar area of outer Delhi Monday morning.
"After spotting the minor alone in her house, the juvenile took her to an abandoned room built in the same building and sexually assaulted her. When the minor began to cry, he fled spot," said a police officer.
Police said the accused was picked up from his house, after a complaint was filed by the victim's family.
In another incident, a two-and-half year girl was allegedly sexually assaulted by a 16-year-old boy in Mayur Vihar area in east Delhi late Sunday evening.
"The minor was playing outside her house when the accused lured her to an isolated spot and assaulted her. However, after noticing several persons roaming in the area, he left the girl crying and fled the crime scene," said a police officer.