org-enforce-todo-checkbox-dependencies

org-enforce-todo-checkbox-dependencies is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means unchecked boxes will block switching the parent to DONE.
When this is nil, checkboxes have no influence on switching TODO states.
When non-nil, you first need to check off all check boxes before the TODO
entry can be switched to DONE.
This variable needs to be set before org.el is loaded, and you need to
restart Emacs after a change to make the change effective. The only way
to change is while Emacs is running is through the customize interface.

You can customize this variable.