When we have to deactivate a 1st level category, all the 2nd and third level categories are also deactivated, which makes sense and is really a useful feature, which avoids the deactivation of all categories one by one.
However, encountering a case where I deactivated a 1st level category then reactivated it, I noticed that it doesn't work the other way around.
In this case, I had 4 second level categories, each with about 5 third level categories, which is not so much. Nevertheless, on bigger category trees, this operation could be very time consuming.
I therefore suggest the addition of a "Activate / Deactivate sub categories" button, under the "Edit" and "Activate / Deactivate" buttons.