How about mattresses?
Do you vacuum them?.. well you should ;) while I was working for a vacuum company (selling door to door, yeah back then lol) we used to test the product on the mattress and show the prospect customer the filter... it was disgusting!
So, here is a tip. Vacuum your mattress, then allow your children to jump on it!! yes, this will move things around and you can vacuum it one last time ;) plus the kids will love it.