LA POUSÉE D'ARCHIMÈDE
This good old principle turned out to be very useful to help my kid get over her fear of water.
In the learning of abstraction there are some concepts which are easier to accept and then learn to play with them.
ZERO THE SUPER HERO
Zero is beyond special and can do all sort of cool stuff like transforming any number no matter how big into a zero if you ask nicely.
A simple way of teaching a kid equations is to tell them that "x" is something that hides the number of fingers that you need to get to three. I told my kid that I called this thing "x", but I could have said "y", "epsilon", "rabbit" or "potatoe"and this would have worked in the same way.