The incident happened at the children's traffic park, located in the heart of the city, this morning.
"The accused, aged around 40 years, forcibly took the 12 -year-old girl to the park, sexually assaulted her and fled," Investigating Officer in the case, Sub-Inspector Kuldeep said.
The victim, a student of Class 8 of a government school, was taken to a government hospital in Sector 16 for a medical examination, the officer said, adding a case has been registered.
Today's incident comes barely over a week after the 29- year-old daughter of a senior IAS officer was stalked by the son of Haryana BJP chief and his friend.