How is it possible that I have not made one of these before?

Diet Coke & Mentos Rocket on YouTube

Based on the well known Diet Coke & Mentos experiments… just do a search for “diet coke mentos” on YouTube.

What an easy way to waste 30 minutes…

… but this does seem like a fun father/son outing at some point.  Here is a nice web page on the science behind the Diet Coke/Mentos geyser effect.