I personally don't think that an assumption that you're being sneaky is because of YOU. It's probably more because that's what many, many people do when they are asking such a question.
For some reason my brain likes to think about tickets, admission, and the whys and why nots of it all, and in my brain, it comes down to enjoyment of the park. A 10 year old, in general, is going to get quite a bit more out of the park than a 5 year old. They will be able to do more, go on more rides, and so forth. Making more use of the park. So they charge in that way, as an "adult", rather than as a child.
Why 10? Who knows. They have to change it somewhere.
Sometimes I think they should go back to free admission and paying per ride...Santa Cruz Beach Boardwalk still does that and it's certainly popular. But then that's kind of a bummer to leave with tickets still in hand, or to run out of tickets too early. (the boardwalk, I hear, has all day wristbands you can buy if you don't want to buy ride tickets, but that's a choice) Great America in Santa Clara has an age and height combo for their tickets...so if you're older but so small you can't go on much, you're charged more appropriately...
Anyway, i've gotten off the track my mind had set for this post.
If I were in your shoes I'd hope for a happy and contented CM at the gates, plaster a big smile on my face, and ask if they can help with my accidental problem, and hope for good things to happen.
