Some soft-sided lunch boxes have vinyl insides which are made from PVC plastic and can be harmful to the hands and food that touch them. One of the most common places parents find child-accessible lead is in vinyl lunch boxes. To check for lead in your child’s lunch box, LeadCheck® offers at-home lead testing kits so you can be sure the lunch box is safe to hold your child’s food.
http://leadcheck.com/keeping-the-home-safe.html
However, old school lunch boxes made of metal can often be a highly desired collector’s item.