Thank you, @nirmal :) I agree that for kids, it can be really difficult to grasp the idea of a probability distribution without even knowing the basics of classical mechanics yet! I know that in most science classes kids get taught about the Bohr model first, which is a good basic approach. However, the concept of energy shells and valence electrons is the necessary basis for all the other things that come next in chemistry in my opinion. Electronegativity, periodic groups, bond types... even oxidation numbers etc. These are the "boring theory" for some, but it actually saves a lot of memorization and a lot of "why?!"s. Personally, when I started studying chemistry, electron configurations was the first thing I learned. It took me ages and a lot of effort, but after that, everything seemed to make sense :)