An 11-year-old girl was sexually assaulted in a supermarket toilet in Warwickshire on Thursday evening.
The attack took place at the Sainsbury's store at the Shires Retail Park in Leamington Spa.
Police said the girl went to the toilet and was followed by a youth who assaulted her. A 16-year-old has been arrested on suspicion of rape.
Officers are trying to trace a woman, who entered the toilets as the attack took place, who may have information.
A Warwickshire Police spokeswoman said the girl, who was shopping with her mother, was left extremely distressed by the incident but otherwise unharmed.
The 16-year-old youth, from south Warwickshire, was arrested during the early hours of Friday and is in custody.