I also run across the "perfect world" problem. At that stage (before they can understand adding various parameters or restraints to the problems) I usually just try to make it funny. It is so important to always have them thinking about the logic of the problems. One time I was teaching systems of inequalities and an example problem in the book was about postage stamps and prices. I asked the kids what they would do if they actually had to pay the postage and figure this out. One responded that he would draw the system on graph paper, shade, find the overlapping region, etc. I said, "Really? You are actually going to take some graph paper and a pencil to the post office to figure out how much to buy?" He chuckled along with the other kids, but the point is clear: getting the students to actually connect mathematical situations to their reality is tough!