while travelling in Bali - our 4.5 year old son was having trouble sitting still and eating his meals (too much going on around him!), so we decided to place a 1000rp note on the table every meal time. If he behaved and ate his food without getting up and down and messing around, he got to keep the money. If not, we kept it. At the end of every day, if he was good for each meal, he ended up with 3000rp (40c), enough to buy himself an icecream for dessert. He was proud that he saved the money to get it himself and we had pain free mealtimes!