I did not think that I would ever find myself suggesting that teaching binary in primary schools could be a good idea. Then I came across a freely available e-book, Computer Science Unplugged, which includes some excellent activities. I especially liked the binary cards where you can start exploring this amazing number system without ever mentioning the “b” word. It is a very short step from making (decimal) numbers up by adding numbers of dots together, to writing them in their binary form. But if that is a step too far, then you can still use the cards to explore various number patterns that are important in computing. For relevant resources, see csuplugged.