The boys are either in the car or are within a couple of miles of the car.
There is no reason to suspect anything different and the comments made here about a car accident or going to the known hazards in the area will be no different to what the police will have said to the parents involved.
The most likely scenarios are car accident, cave accident or walking accident. These are not wild speculations. They are realistic concerns.
The police knew where to look from the phone data and a member of the public presumably alerted by the publicity contacted the police about the car.
The police wanted the public to act and be involved or they wouldn't have put a media call out.
It's important to understand these risk in order to prevent incidents in future.
We will find out in due course what has happened.