LILLIE-BETH'S ANSWER: Yuk! — At least for the other shoppers. For the family, it sounds like the displays made them feel right at home. That's too bad for the store because it won't sell much bedding if everyone sees that behavior and thinks they are buying used sheets. Thank goodness bedding comes in (mostly) sealed packaging, as I am sure what you witnessed wasn't as unique as we hope it is.
However, as disgusting and self-centered as the family's actions are, I don't think it becomes your problem unless they are in your way or throwing things at you. And if they are, then you can ask them to move or stop. At the very least, if you see children wandering far away from their parents, you can nicely ask if them if they need help and then guide them gently back to their mom or dad.
If the store managers/salesmen are aware of what's going on, then it is up to them to ask the family to get off the beds or to stop messing up the display. But their training may not allow them to question customers. If that is the case, then everyone has to endure and hope the parents don't get too comfortable and take a nap while the children play. As a last resort, if you want to help the sales clerk, then let a manager know that they're interfering with your ability to shop.
HELEN'S ANSWER: Of course, we wish that people would control their children and themselves when they are out and about. The clerk needed to politely take charge and either get them out of the store or direct their attention elsewhere.