Two 11-year-old boys were attacked by a man in Abington Park after he walked past with his daughter.
The attack happened on Saturday, between 2pm and 2.30pm.
Police say the 11-year-old boys were part of a larger group in Abington Park and started joking around when a girl walked past with her father.
The man then began chasing the group and caught up with two of the boys.
One of the boys was pushed to the ground and punched in the chest, when the second was pushed against a fence and slapped.
The attacker is described as white man in his 40s, stocky build, 5ft 8ins tall, grey hair with a goatee, wearing white trainers, light coloured jeans, black jacket and red shirt underneath.
The incident took place near to Park Avenue South, by the crossing.