Sheep and children both learn very early to recognize their shepherd's voice. Shepherds in Israel still bring their flocks together at watering holes at the end of the day just as they did in the time of Jesus, letting the sheep mingle in a great confused mass without a worry about separating their own from the tangle. When the time comes, each shepherd calls out a particular word, sound or whistle and his sheep come and follow him into the corral for the night. Sheep know whom they belong to. They recognize their shepherd's voice and it is the only one they will follow.
Children also learn very early to recognize their parent's voice.
Hold a small infant sometime and watch what happens when the mother's voice is heard. A child knows the parent's voice very early and brightens at the sound. Children and sheep share an even more important characteristic. They can not be driven. They must be lead.