An extensive search has been launched after two young boys were spotted out alone in the early hours of Wednesday morning.
Nottinghamshire Police said they received a call from a man who saw the children, believed to be aged between four and six, in Bulwell, Nottingham, at about 12.30am. They were not with an adult, and no children have been reported missing.
A spokeswoman urged any parents or carers to get in touch if they thought their children may have been out in the area overnight.
Both are described as white with dark hair. One is about six years old, of slim build, and around 4ft 6ins tall, wearing a dark-coloured pyjama top. The second boy is aged between four and five years old, around 4ft tall, of slim build, and was wearing a blue pyjama top.
Police said more than 50 officers were involved in the search for the boys after a taxi driver reported seeing them at 12.30am. The force said the second sighting of the pair near an underpass in Newmarket Road was reported a few streets away at about 5.30am.
Police had still received no reports of missing children, but said they were concerned for the welfare of the boys because of their young age.
A spokeswoman said officers had been searching streets, gardens and outbuildings, were contacting local schools and talking to teachers, and viewing footage from CCTV cameras in Bulwell.
Chief Inspector Matt McFarlane said: "Our priority is to establish if these two boys are safe and well and we are continuing to conduct a comprehensive search."
Anyone with information should contact Nottinghamshire Police on 0300 300 99 99 or call Crimestoppers anonymously on 0800 555 111.