....and remind them to NOT TOUCH ANYTHING BEFORE ASKING TO DO SO.
I don't mind if a kid/young adult handles the merchandise, after asking. But, please, teach them to ask first. Unless I know the dealer/person that has the items for sale(and they know me), I always ask first out of courtesy.
I don't bring my 2 boys(7 year old twins) to the gun shows for this very reason. They have NO self-control when it comes to things(especially guns) that are shiny or cool-looking. When they are older and have learned a little more self-control, it will be great to bring them along to see all of the cool stuff(and people) at gun shows.
So, yes bring them, but teach them to be respectful of other people's property, and that they don't really need to pick up every single item on every table.
I suppose this goes for adults, too.