Curiosity for children usually takes the form of exploring how things work. That is an active process. For example, with the apparatus pictured below, the children have to act on it to see how it works. (More about this apparatus can be found in the following two posts: Totally different and Channel, tube and homemade plunger.)
The picture below shows the apparatus with an added feature: a cardboard chute taped to the incline. One hole is cut in the top and one at the bottom. Yet another hole is cut at the bottom of the chute so it directs the sand into the original hole at the bottom of the apparatus.
The picture below shows the apparatus with yet another added feature: a cardboard chute taped horizontally to the top of tower box.