It's 2-4 rows of chairs in an open area. The viewing area along Rivers of America is a raised terrace with a walkway down below where people stake out places hours in advance. Your area is between the stairs that go down to the waterside, all along this raised terrace, in front of the big light poles that raise up to project the lights. There is plenty of space to walk to the back and stand to watch, if you couldn't see, but I don't think you'll have a problem. My DD 5 could see just fine from the second row, even if she had to lean *fractionally* now and then to maybe see a figure on the stage around the person in front of her-- but not at all a really "blocked" view. Your DS could certainly kneel on his chair if he had to, but he probably won't have to. That would be my guess, judging from our experience 3 weeks ago.
It's not in a stadium like in WDW.
Hope you have a wonderful time! We really enjoyed it.