This simple smoothie recipe is currently our favorite fast breakfast. My older two can make it themselves. (I pour up, though!) And we've only had one major mess so far: the two year old assistant pushed the blender button without permission. The blender was already full, and the lid wasn't on. Even that incident wasn't as bad as it could've been. Anyhow, we love it, and it gets you just as far as a bowl of oatmeal!
4-5 bananas
1/2 cup peanut butter (more or less--we never measure it)
1 quart buttermilk or yogurt
Add as many ice cubes as you can fit one by one while blending to top it off and chill it out.