Little seven introduces the concept of "seven" by interacting with seven of a variety of things, some of which are grouped and regrouped to demonstrate adding and subtracting.
Little Eight introduces the concept of "eight" by interacting with eight of a number of things, some of which are grouped to further expose the reader to subtracting and dividing.
Little Nine introduces the concept of "nine" by interacting with nine of a variety of things which group and regroup to demonstrate principles of adding and subtracting.