Just use a cup or a small bowl to shape the rye-bread. It`s great for small children, cutting the crust off so they may better get it down and much more fun to decorate the bread in a different way.
It is only imagination that sets limit to what you can decorate the bread with. Salad, tomatoes, avocado, banana, all kinds of spread, apple slices and a lots of other possibilities. Hummus or peanut butter along with raisins, nuts or cucumber. Just ask the kids what they like and make the lunch bow together.