A gang of school-age teenagers robbed a woman from Portslade and left her boyfriend with a broken cheek and broken ribs.
The 12 to 15-year-olds surrounded the couple as they walked up Boundary Road, Hove, towards Portslade Station.
By the bus stop near the New Church Road traffic lights they told the 29-year-old woman to hand over her handbag before one of the girls in the gang snatched it.
Sussex Police said: “The children ran away and the woman’s partner chased them to try to recover the bag.
“When he caught up with them he was surrounded again and knocked to the ground.
“Members of the gang then punched and kicked him while he was on the ground.
“The gang took the man’s backpack from him and ran down an alleyway between Franklin Road and Vale Road in Portslade.”
The 26-year-old Worthing man suffered a fractured cheekbone and broken ribs in the attack.
Among the items stolen in the robbery were bank cards, mobile phones and the two bags.
Sussex Police said that the gang included more than a dozen children and that they robbed the couple at about 11.15pm last Friday (21 June).
Detective Constable Rowan Carter, of Brighton and Hove CID, said: “This was a terrifying unprovoked attack on the couple who were simply trying to make their way home.
“We need to speak to anyone who could identify any of the children involved in this violent and brutal robbery or who saw what happened.”
Anyone with information is asked to call Sussex Police on 101.