Create A Toy Zone With Masking Tape
No longer do I run the risk of treading on a piece of Lego in the dark, no longer do I find marbles under sofas and no longer do we have to fashion Monopoly pieces from tin foil because the originals are missing in action.
When they were small, however, they used to spread everything over the largest possible area and it drove me NUTS!
If your young kids are the same, and you don't have the luxury of a dedicated play room, then you might like this possible solution that I ran into over on ParentHacks - mask off an area of whichever room you want to keep under 'control' with something like masking tape, gaffer tape or similar and make it 'law' that all toys must remain within the taped off zone.
Genius, brilliant, cheap and, I imagine, very effective.