I've never seen more than 2 people at a design station, so I don't know that all 4 of you could be at the design station. And the height requirement might preclude your kids from participating at all.
We did this at rope drop twice during the past week, and we were the first ones on the ride (one day we were on at 8:50, while everyone heading to Test Track was held at a "rope" at the Innoventions breezeway until 9:00).
For two 11-year-old grandsons, Sum of All Thrills is their current favorite of all WDW attractions. One day, they did the attraction twice in a row, and the other day, they did it three times in a row (each wait being no longer than the time for the pre-show to end for the group ahead of them). Then it was on Mission Space, followed by Test Track with FP+.
Yes, there is no FP+ for this, nor are there wait times listed in My Disney Experience.