Good kids shouldn't have too hard a time getting the rangers' number.
Any responsible adult would direct three helpless young boys to the rangers if they were worried about seeing things in the woods.
Try finding a responsible adult. (It's harder than it sounds.)
More specifically, look for a responsible adult that's authoritative enough to carry around the rangers' information.
Go to the 'New Frontier's Gate' at the very top of the map, and tell the guard about seeing something strange in the woods.
He should give you the 'Ranger Flyer', exactly what you need. Return to these hints.