MY children were given these corn bags when they were 2 years old and we have been using them since (they are now 15 years old). I have never had any vermin or anything in them unless you tend to get mice in your house. I like the smell of corn when it is warmed up.
I make sure that we do NOT store them in plastic bags...they just sit on the closet shelf when they are not being used to warm someone's toes, or put on an achy shoulder, or on a tummy with cramps. They are great. I have given them for gifts for 10 years now...