First you need to make sure that your own understanding is reasonably correct. Otherwise you'll be doing more harm than good. You can start watching some introductionary videos like this one: https://www.youtube.com/watch?v=zKb3QRyIDnM. You can google this and see which videos you like. You may even be able to watch some with your son together.
The key points are
Energy is the ability to do work: Lifting something light is easy. Lifting something heavy is hard. You need energy to lift something, that's where the work comes from. If you lift something that weighs 2kg you need twice the energy as if you lift something that weighs 1kg. You can do a fun exercise with your son, lifting up a few objects and then throwing them on the scale to compare.
Energy also adds up. Lifting an object 10 times requires 10 times the energy as lifting it once. Again, that's something you do with your son together.
Energy can be measured. There are multiple units for energy: Joules, Calories, kWh etc. They are just different names for the same thing. Energy that you body uses comes from food. The more calories are in the food the more energy you get and the more you can lift. You can sit down with your son and look at some food labels.
An electric car needs energy to move. The longer it moves, the more energy it needs. This energy is measured in kWh.
Energy comes in all different types of form: food (chemical), electricity, heat, sound, motion, light, etc. It can be converted from one to the other but it's never created or destroyed. The term "energy generation" is actually a misnomer!!
Examples: Your body transforms food energy into motion energy. An electrical car transforms electrical energy into motion energy. A solar panel transforms light & heat energy from the sun (which you can feel on a sunny day) into electrical energy. A wind turbine transform motion energy of the wind into electrical energy etc.
You can play a game with your son where you look at pictures or anything at home or outdoors and search for examples where energy is converted from one way to another. If you see a car go by: fuel energy (chemical) is converted to motion energy (it moves) and sound energy (it's loud). A squirrel climbs up a tree: it converts food energy to motion energy, etc. Pretty much everything you see that changes in some way form or shape involves some energy conversion.