Several theories have been put forth as to why kidnapped children do not attempt to escape or contact family members. I have become very familiar with these theories and concepts in my research into the life of the young lady we know as Sharon Marshall.
Children are by nature very trusting, dependant, and much more resilient than we as adults give them credit for. The pedophiles who kidnap children understand these concepts and make the most of them. Thus it is that they either live far removed from other people (Steven Stayner) or move constantly (Sharon Marshall). This isolates the children, forcing a dependence on the kidnapper. The kidnappers use all manner of pyschological tactics on the children to enforce this dependence-lavishing them with gifts and praise, then withholding any affection, for instance. The children, as a defense mechanism, suppress any thoughts of their prior life.
The kidnapper may threaten the lives of the child's loved ones, telling the children that if they attempt to leave or contact anyone they (the children) wll be responsible for what happens to their family-often going into graphic detail as to what will be done, constantly reinforcing the notion it will be the child's fault.
Further, the kidnapper may shame the child into a complete mental withdrawal from any thoughts of their prior lives. The child may begin to believe that the kidnapping (and any ensuing abuse) is their fault, and that their family will be ashamed of them for what has occured. The kidnapper will reinforce the thoughts of pain the family has suffered because of what the child has done, and that the pain will only be greater if the child returns to the family. The child may grow to believe the family does not want any contact from them.
These monsters who kidnap children will use any form of mental and physical torture at their disposal to keep the child in line.