My kids also "have a lot of stuff" as you say. I've been struggling to find a maintainable well-organized storage solution for it all, and we're finally getting there. Since my kids are quite young, their "stuff" mostly consists of small toys. To maximize their closet space, we installed additional shelving from Home Depot. We've lined many of the shelves with various sized plastic tub containers (adding a label to indicate what belongs in each). To maximize the use of the space in the bins, we sort the groups of little toys within using see-through zip-close mesh fabric bags (www.KidsKlutterKatchers.com), which has also significantly reduced the chaos. Anything that doesn't fit in the closet is a candidate for purging.