The first smoothie-- SCARY FRUIT SMOOTHIE-- is made by a couple of charming children from Ireland. Their smoothie involves cranberry juice, banana and raspberres. The boy says that any fruit is possible but that raspberries make it look more like blood. I think your little goblins might enjoy making this. They float a couple of marshallow eyeballs in their drinks (optional)
The second smoothie for kids by kids is a very healthy smoothie made by one little witch. It uses diced pumpkin, mango (she calls it canteloupe but it says mango under the video), carrot juice, and banana. There appears to be a little container of honey that doesn't get used-- it is optional I guess. This smoothie really does look quite tasty. (If your kids don't like pumpkin, I'd suggest just going with the other ingredients, all orange).