Around 50,000 cases were recorded between April 2012 to March 2014 but the report suggests that the actual number is nearer to 450,000.
Much attention has been focused on child abuse in institutions but most happens within families or their trusted circles, the report said.
The government said it was looking at how authorities dealt with abuse.
The report found:
- Two-thirds of child sexual abuse took place within the family environment or the close circle around it
- 75% of victims were girls
- Abuse was most likely to have occurred at about the age of nine
- Victims often did not speak out until adolescence or later, when they recognised what had happened
- Even if a child did tell someone, often the abuse did not stop
"We must now wake up to and urgently address the most common form of child sexual abuse - that which takes place behind the front door within families or their trusted circles," she said.
She called for urgent action from government to prevent abuse, and for more training to help teachers, social services, police and other professionals identify abuse early on.
"There are always signs. Mental health problems, children can become withdrawn or show overly sexualised behaviour. If you know the child it will be obvious to see changes in their behaviour," she said.