Here is an example of what happens when you ask the three most important questions:
The original goal was to design the best wand for creating the largest bubble. But since the child is being asked to observe and theorize, it becomes about more than that. The child is actively making new discoveries based on observations. The most important part is how he revises his theory based on a new observation. Watch this 11 second discovery followed by a 44 second discovery!
By asking these questions, this becomes a unit that is about much more than just creating bubbles. It becomes a unit about designing experiments to learn, and adapting your ideas based on new information.