You have a lot of good suggestions in the earlier posts. Do not worry about inductors, and capacitors. A six-year old is not (likely) ready for Ohm's law, impedance, phasors, and differential equations.
Regarding touching a 9 volt battery to the tongue. This seems harmless and I did it hundreds of times, but when I got older, I used to listen to the radio with a rechargeable 9-volt battery. The instructions on the battery warned, do not carry in your pocket where coins can short the battery and produce burns. I never got burns but they did get uncomfortably warm. I would not want that on my tongue.