From a CNN article on the Dugard kidnapping and abuse case:
Aside from the physical abuse of children, experts say perpetrators find ways to manipulate the minds of the children they are abusing.
"Sexual abuse doesn't happen in silence," said Karen Duncan, a clinical therapist. "Things are said to the child before, during and after. Offenders say things in a purposeful way -- to convince the child what they're doing is OK and acceptable. The children do not know the laws. They really don't know this is something that's not supposed to happen."