ive got two tables a form and sub form

what ive noticed on each record that for main form creates is stored on the main table, however if the main form goes onto the next record and nothing was changed on the subform, the sub form table does not create a record

is there a way so that the subform stores information to its bound table even if its not been changed.
i would preferebly like to have a checkbox that by default is ticked on the subform but if the subform changes for the checkbox to be unticked, this was i can see from a report whether the the form has been edited or not

thank you