Mustard Greens with Garlic and Mustard Seeds

Calcium has been on my mind a lot lately. We don't do dairy (or soy), which cuts a lot of calcium out of our diet. Or does it? The more I think of all the greens we eat around here, the less concerned I am about our calcium intake. I am challanged as to how to get the girls to eat calcium-rich greens like DH hnd I do, but they eat sardines, which are one of the foods that are very high in calcium