The voice is raspy. If severe, your child can do little more than whisper. A cough is often associated with the hoarseness.
Allergies can also cause a raspy voice from sticky secretions.
Your child should gargle with warm water and suck on hard candy or cough drops several times a day. Younger children can sip warm liquids like apple juice. Encourage your child to rest his voice and avoid the voice strain that comes from yelling and screaming. Encourage him to talk as little as possible for a few days. If the hoarseness gets really bad, have him whisper or write notes.