Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
Whistle register
Many babies and small children regardless of sex can produce sounds in the frequency range of the whistle register without any conscious effort. Typically, the whistle register in children extends from the soprano "high C" (C or 1046.5 Hz) to two Gs above (G or 3136 Hz). Some children, however, can produce pitches that surpass the upper limit of the keyboard.