There will be some events where the decision has to be that juniors below a particular age are not permitted to run unaccompanied (e.g., as per rule 11.20, for juniors aged under 16 years of age on the day of the event, courses must not have any routes that might plausibly require them to cross roads with significant traffic unless appropriate traffic management arrangements have been put in place).
Image credit: Rob Lines.

Below are a number of safety considerations event officials should bear in mind for night events for all participant groups(!) but especially where juniors will be allowed to compete unaccompanied: