Without meaning to advertise a certain type of building blocks, I would like to show you something fashioned from a pin on pinterest which deals with a number of problems. Number one problem is TINY pieces, lost on the carpet.
Now they are easily contained, and the minky fabric is a delight to sit on. I tried a drawstring first, but it's too bulky to cinch up, so I sewed eight tabs which can be collected with a carabiner, and YAY! There's also a pocket for some set booklets and building ideas.
One of many projects around the house with a four-year-old.