Well, maybe some of your thinking is correct, but don't forget, those 'older' kids will have families with little children that will bring them back to Disney!
I, and my children, are far from little 'kids', but grandchildren will keep you going to Disney. Also, we are also still 'little kids' when we see the Mouse!
There will 'always' be new families going, as maybe a few others leave, that 'may', or 'may not' be back.
There is 'no' shortage of families with children - reference the huge crowds!!!