Hearing your child tell you that he or she has suffered abuse of any form is devastating to a parent who loves them so much. It can give you the feeling of being a failure as a parent, because you couldn't protect them enough. It can also be extremely upsetting because more often than not, the abuser is someone you know. They may even share the family home, maybe it's your husband or your wife who is the abuser. That adds an entire new facet to the pain of the disclosure. But you must keep your own feelings in check for the moment and focus on your child.
He or she will need you to do several things to improve the chances that they will come through this changed, but able to heal properly. The first thing they need from you is belief in the story they are telling you. Keep in mind that it has possibly been some time that they have been dealing with this alone, as they tried to figure out how to tell you what has happened to them. Do not question the truth of what they are saying in the slightest. It is rare for a child to invent stories of abuse, especially sexual abuse.
Your demeanor should remain as calm as possible. If you fall apart, the child will not be able to feel protected and supported by you. They need to be able to feel like you are going to be okay and they are because you're there for them. For victims of abuse, there is a feeling of helplessness that is terrifying. They may also have been told that you wouldn't believe them or that you wouldn't be able to protect them, so that must be dispelled immediately.
Your child needs reassurance right now that you love them. Hug them or allow them to sit on your lap, whatever is age appropriate and doesn't seem to bother them at the time. Tell them in no uncertain terms that they are the most important person to you, especially if this is a parent that is abusing them. Tell them that you love them and that they didn't do anything wrong. Tell them you're proud of them for telling the truth about what happened. These are things that your child needs to hear from you.
Contact the proper authorities. Allow your child to tell you what happened, but don't ask too many questions. This may go to court one day and you don't want to be accused of coercing the child into saying certain things. Contact a counselor who is trained in this sort of trauma. Contact the child's doctor to get him or her in for a check-up as soon as possible.
Child abuse is a very serious matter that will impact the rest of the victim's life. How you respond to your child's disclosure will have a tremendous effect on their recovery from this and their self-image in the future. No one is perfect. If you do your best at this emotional and shocking time, you will have done your job. Move forward into a better life, protecting and nurturing this most precious son or daughter.