The ‘suspicious incident’ took place on Thursday evening.
The boys were outside Edgbaston House, in Sedgley Close, Somers Town, when they were approached by a man who talked to them, pushed one and then followed them briefly when they ran away.
The incident occurred between 7pm and 9pm.
A spokesman for Hampshire police said: ‘Officers are making enquiries and will be conducting patrols in the area.
‘We are keen to speak with anyone who saw anything suspicious or who can assist with our enquiries.’
The man is described as white, with black hair. He was wearing a black t-shirt, black shorts and a black mask.
A police spokesman added ‘Officers are also keen to speak with a man we believe intervened in the incident. He had blonde hair, a blue t-shirt and blue jeans.
‘If you can assist our enquiries, you should call 101, quoting the reference 44220239894.’