Too much stuff

Trying to help my d-i-l clear the chaos of her home prior to a new baby - and not succeeding. Fact - they have more stuff than most houses can hold. Notice on shows like HOUSE HUNTERS, 20 & 30 somethings routinely complain about closet and storage space being too small. My kids and grandkids have 10 times the clothes, shoes, toys,etc. than we hadat any time in our lives. Most of the stuff is unused, there's just so much they can't remember it all. And the clutter grows with each shopping trip.