I started by reviewing simple fractions. I drew apples on blank index cards and then cut one in half and one in quarters. This way the girls could easily see there are 2 halves in a whole and 4 quarters.
I also made ten more of these apple cards and taped them to the piano (the girls thought it would make a good apple tree).
From there they took turns collecting the number of apples I told them. Once they had the apples I asked them to give a certain number to their sister and then tell me how many they had (subtraction). I also asked whoever received the apples how many they now had (addition). This was repeated over and over and over, refilling the tree several times. While I'm sure they didn't memorize any of their addition or subtraction tables; I do think it helped to cement the idea of addition and subtraction (what we really needed to work on).
Need other activities to go with this book; check out these: