It can be a heart-stopping question for parents: "Where is my child?" In parks, at beaches or in any public setting, your kid can wander out of view in an instant. But technology can provide some peace of mind in the form of a lightweight GPS tracker that can last a day or two on a charge, and offers frequent and reliable updates on your child's whereabouts. Some of these trackers are watches, some are meant to blend in with your child's backpack and work in the background, and some even give you the power to detect possible danger in your child's vicinity.