My opinion of course, but I think Space is harder on adults than it is children. I used to be able to ride and ride with no problems. Now I find it jerky. Or maybe I'm just getting old. =( I'm taking my niece and nephews in Oct. My plan is start with Barnstormer, 7DMT, and then Big Thunder. Figure I'd start them off small and work up to Space instead of going right for that one off the bat.
Good approach. If they don't like the big one you have to be careful and they will not ride any of them. Starting small and going up you get to see their limitation.