"Special"

My wife started an interesting incentive program for Jaden and Jacob a little while back. On a given day, the boys can earn a "special" through good behavior over the course of the day. If they start to have problems, she can remind them that they will lose their "special" if they don't correct themselves. Our kids are into the Matchbox cars, so, she procured a box of these with around 100 cars that we can take out and give to them on these various days. Overall it works pretty well, but considering we have almost 100 cars to go, and I don't like giving them more than 1 day a week where they can earn them, that is many weeks of cars in inventory. I hope that they will continue wanting their "special" car a long time.