To ensure my two sons, Nathan who is 5 and Toby who is 3 get a balanced (brainwashed as Christine would say) education, I recently got them a basic electronics kit to help teach them some simple electronics principles.
The kit I ended up is a Snap Circuits 300, the kit uses plastic tiles, each has a different function, some are wire connections, some the resistors or lights or other components. The SC300 box has 300 different electronics experiments that can be made with the parts, from simple light and switch circuits, to more complex sirens using IC’s and even an AM broadcast radio. The kit allows expansion boxes to add more projects into the future as well.
The kit is designed for older children, but even so, my sons have a ball with me helping them build the experiments. The components on the tiles all “snap” into place and are big enough that little fingers can easily build the different circuits. The kit has a plastic base with a grid that is used to align the parts. They enjoy checking the circuit path, and we talk about what will happen along the way, what different components will do to the circuit. We even get the multimeter out and measure things along the way to help explain whats going on. Though their favourite of the experiments is called the “UFO” a fan that spins on a motor and take off/flys into the air when the power is turned off.