Please .. that is just semantics .. Disney thinks of kids 3-9 and adults as 10+. Disney has kids meals for kids 3-9 and adult meals for 10 and over. Which makes the Buffett restaurants CRAZY priced once your kids reach 10 - 40 dollars for a 10 year old - ugh! I saw people in the Chef Mickey line lying about their kids ages to get the lower price ... You could tell because the Mother kept shooshing her kids .. The lady asked what ages oh they are under 9 and they were like Mom and she was "shhhh".. of course this might happen if you set the cut off to 12 as well. There is a big difference between paying 40 for your kid and paying 20 for a meal. The actual Park tickets aren't that much difference .. For a 6 day hopper on
UT its like 306 compared to 287 .. like 20 dollars difference again but you are talking 6 days of tickets. The real killer is the meals.
Anyway Ages at other parks:
At Legoland kids are ages 3-12. (Better than Disney)
At Hershey park kids are 3-8. (Worse than Disney)
At Dollywood kids are 4-11 (Better than Disney)
Like PP.. Kings Dominion, Cedar Point, etc... Go by Height - 48" .. of course Kings has a good deal right now that anyone can play the Kids price - 37.99 - great park too.
(Usually the height is worse than Disney - my short daughter was 48" by the time she was 8)