org-checkbox-hierarchical-statistics

org-checkbox-hierarchical-statistics is a variable defined in `org-list.el'.
Its value is

t

Documentation:
Non-nil means checkbox statistics counts only the state of direct children.
When nil, all boxes below the cookie are counted.
This can be set to nil on a per-node basis using a COOKIE_DATA property
with the word "recursive" in the value.

You can customize this variable.