The incident occurred at around 7.25pm on Thursday 16 May on the footbridge spanning Childs Way between the Milton Keynes Xscape car park and Pencarrow Place in Fishermead.
Two young girls and a boy approached the footbridge when a young male, aged in his mid to late teens approached them.
The boy produced a weapon which appeared to be a pistol, from his waist band and raised it.
The three children ran off and they heard a sound which appeared to be a discharge of the weapon as they left the scene.
The offender is described as a white teenaged boy aged between 16 and 20 years old, around 5ft 6ins tall with an average build.
He had dirty blond hair and was wearing a light grey hooded top and light grey bottoms.
None of the children were injured during the incident.
Investigating officer Detective Constable Scott Dempsey, of Force CID based at Milton Keynes police station, said: “I am appealing for anybody who witnessed this incident to make contact with us.
“I am particularly looking to speak to a specific witness - a woman who was seen on CCTV and appeared to have intervened and spoke to the offender. I believe this woman will have crucial information to assist in our investigation.
“I appreciate that this is a concerning incident, but there is nothing to suggest any wider threat, and I believe the weapon to have been a starter pistol or something similar.
“We are investigating this incident thoroughly to bring the offender to justice.
“I am urging anybody who has any information, or who knows who the offender is, to contact 101, quoting reference number 43190147498.
