Ok, how safe is the actual place? Chavvy may be fine , there could be lots of grans it mums hanging around in a way there would not be in somewhere more upmarket.
If you let them go, make sure
They have z few rules to keep
They must be back at x time.
They must get the x bus back and ring you beforehand when they arrive to tell you which one
They must under no.circs be separated, even if they have a row, or meet prince charming, or fall over
Have charge on their mobiles
Update you if there is something worrying
Not talk to strangers/ accept drinks or lifts ( esp the last)
Keep the emergency money you have given them safe
Know what to do in a crisis. ( shout fire, more people will come and look than if you shout help, find a policemen or s shopkeeper).
If they can repeat the rules to you, then let them go.