the question on the child's return is "CAN" someone (such as your parent) claim you as a dependent.
Not "DID" .......
there's no requirement to claim dependents but that doesn't mean the child can answer NO to the question on their return
the tax laws (IRC code section 152) has certain tests for determining whether a person is a qualifying child or qualifying relative. if they are then they CAN be claimed as a dependent.
