In the Red Kit, you'll find a MaKey MaKey board, a thick red USB cable that powers it, 6 thin white connector wires (a.k.a. jumper wires, with little pins on either end) and 7 Alligator cables (lots of colours, with little serrated jaws on each end).
In the Blue Kit, you'll find an Arduino Uno board, a black USB cable that powers it, a twisty switch called a potentiometer and a variety of little LED lights (called Light Emitting Diodes - a diode is a 2 legged thing).
The Arduino board is a small circuit board. It has a small chip on it (called a microcontroller) that can be used to add interactivity to projects. Arduinos are easy to program, using your normal computer, but you'll need this software to help your computer talk in a way the Arduino will understand.