Our son is just like I was at his age: the only thing he will eat for lunch is a PB&J sandwich. We use natural crunchy peanut butter (Trader Joe's is the best), and good quality strawberry jam. But the bread is the most important part.
While the No-Kneed Bread makes delicious bread, it's not good sandwich bread. For that, I turned to the Bread Lover's Bread Machine Cookbook. Ages ago, my friend recommended this cookbook to me and it is awesome. Trying a few of the recipes, the "Light Whole-Wheat Bread" was almost there...but it was a bit too light, and I found the volume measurements to be a bit inconsistent. When baking, having a scale is essential. So I boosted the amount of whole-wheat flour, tweaked a few of the ingredients, and converted the volumes to weights, and voila!