I got these cute little baskets at the dollar store (the one where everything really does cost $1) and I keep them on the steps for all the stuff that makes its way downstairs that should be upstairs. Once a week or so, the kids have to empty their baskets. I sometimes get mean and dump them on their beds and tell them to get busy, but I don't do that very often, I promise.
I did not intentionally get two different sizes, I thought they were all the same, when I took them out of the package I noticed Zoe's was bigger. Actually it works out because she is the one who has the most migrating stuff. Oh and I do help Tanner with his, obviously he can't do it by himself yet.