Dual addition and multiplication
But relations to arithmetics are to be built: The pupils must see how simple (and familiar) binary addition is. One plus one is still two. Only the two is written in a different way! And how enviably simple is multiplication! It goes the "Hamlet way": To write and add or not to write and not to add, that's the question... Most simple is the "multiplication table": One by One is One, all else is nought. Essential are comparisons with decimal calculations to show the binary way to be allright. Here I leave away subtraction and division, that is too sophisticated now, it will be shown later).
I rather tell of Leibniz, who had dealt with the binary system and by this occasion discovered the system of antique chinese number signs.
move on