Most kids have favorite toys. They're always winners and are loved over and over again. That usually means the other toys get ignored, at least from time to time.
Hiding toys away for three to six months is a great strategy to see if your kids still want them. Pack some up in a plastic bin or box; store it away in a closet or storage area. If you're feeling extra ambitious, stick a label on the side that says which toys are inside. Then, if a specific toy is asked for, you can find it quickly. Otherwise, bring the toys out in a couple months. Pack up different toys, and repeat the process. It's especially great when you don't have a ton of space for toys, but do have some storage room to spare.
Think of it as if you're swapping out seasonal wardrobes, but with toys!