A person commits a crime of the third degree if he knowingly:
a. Restrains another unlawfully in circumstances exposing the other to risk of serious bodily injury; or
b. Holds another in a condition of involuntary servitude.
The creation by the actor of circumstances resulting in a belief by another that he must remain in a particular location shall for purposes of this section be deemed to be a holding in a condition of involuntary servitude.
In any prosecution under subsection b., it is an affirmative defense that the person held was a child less than 18 years old and the actor was a relative or legal guardian of such child and his sole purpose was to assume control of such child.