This will sound dumb but a few years ago my uncle went camping/pig hunting in the middle of the bush in the Northern Territory and in the middle of the night heard whistling and rustling off in the distance. A history of family dumb assery (especially on that side of the family who live in the NT) meant he decided to brave the darkness and go for a walk and follow the noise. Eventually he caught up to it and in the distance saw a bunch, like ten or so, of little people sort of running around with each other. He said they were the height of young children but had adult-like features. My guess is it was a group of indigenous kids and his eyes were playing tricks on him late at night. Still would be pretty creepy to hear whistling in the bush at night.