janthea this is an extremely rare occurence and when such situations arise, the police go full pelt at it and will not cease until they have some results. They'll have convened very high level 'gold' meetings, bringing in all the relevant agencies, and briefing people who manage workers who are out and about on the streets like postal workers, delivery companies, council and road workers, to try and pull information together. Every registered sex offender, and those who are known but not registered, will be brought in to be questioned about their whereabouts when these incidents have occured. Police leave gets cancelled and they'll be going flat out with the Chief Constable, MPs and Council Leaders leaning on them to report back information. Resources get redirected, so people reporting burglaries will be complaining no-one has been to see them! If it's a gang, someone will know something - gang could mean 2 or 3 people in this case - likely to be men, and they would need to be inobtrusive, so more than 2 or 3 would attract attention.
I once supervised a man on parole who has attempted this sort of thing, and was very worried when I heard of an incident, so phoned the police to name him - as soon as his car was described, the police did a trawl of every similar car and went out to account for every one. He travelled 25 miles to commit his offence, but they still found him - he went to prison again for 5 years.
I hope the children are ok after such a frightening experience. Their parents must think their worst nightmare has happened. Rest assured that the police won't rest until this is detected.