This is how I sex all types of fowl.
Take a thin string or some fishing line, about 1 foot long. Tie a bolt, or washer to one end.
Hold the chick in your hand, on it's back, with belly up. Hold the string by the end, and dangle the bolt over the chicks belly, about an inch above.
Hold it very steady. The bolt should start to move on it's own. If it swings in a circular motion, the chick is female. If it swings straight, from the neck to the tail, then the chick is male