Vegetable juices and vegetable smoothies are all the craze these days, and for the best of reasons: drinking them is like having a liquid multivitamin straight to your blood stream! As good and necessary as fiber, chewing, and all the regular process of eating wholesome foods may be, when you take out the fiber of fruits and vegetables (as you do with juices), or pre digest them by turning them into liquid in a blender (as you do with smoothies), the nutrients go quickly into your system, and your digestive system a rest from the daily grind.
The big question is, how do you get kids interested in these powerful drinks? A good way is to keep the stronger greens in slower doses until they start getting used to their taste. Another thing kids love is the creaminess factor, for which both bananas and avocados are a great choice. Try to stick to avocado as much as possible though, as you don't want the smoothie to have too much sugar in it.