In general Peru is a quiet and safe country. The Peruvians themselves always warn the tourists to be careful with their belongings and carry the camera over the shoulder and not on one shoulder. Theft is a rare event, but you better keep this in mind to avoid any unpleasant situation.
You must be very careful in Lima: use only official taxi-cabs, do not wear jewelry and do not go to districts that are not recommended to visit. In any city you can ask the employee of the hotel or taxi-driver what districts you need to avoid at nights. These are rational precautions that are actual in every country.
We look forward to working together to turn your dream trip into lifetime memories!