The nesting of sub cards in the kudos boards is amazing, it allows to structure the work and break it down into small activities.
The idea to have a checklist, where each item is a sub card, is absolutely great, it's just missing a tiny little detail:
If you create a bunch of sub cards, e.g. 7 of them, in the parent card it shows ist as "7 tasks".
But if you tick off (complete) some of them, e.g. 4 out of 7, it still shows "7" in the parent card.
I suggest that a second number is added, which is the number of completed tasks.
If you create 7 sub cards, like in the example above, the numbers should be "0/7" initially in the parent card, when 4 task are completed, it should be "4/7" and if all tasks are completed, "7/7" respectively.
Trello does it like that, BTW :)