A family gratitude ritual works best when it fits naturally into something the household already does together, a shared meal, a car trip, or the last few minutes before younger children go to sleep. Borrowing an existing moment tends to outlast a ritual that requires everyone to gather specifically for the purpose.
One well-worn version has each person name one good thing from the day around the dinner table, kept brief enough that even a tired or reluctant participant can manage it. The brevity matters more than the depth, since a short ritual repeated daily tends to matter more than a long one attempted occasionally.
Over time, these small rituals seem to do double duty: they build a habit of noticing good things, and they give a family a small, reliable moment of connection that exists regardless of how the rest of the day has gone, which turns out to be valuable in itself.