I wholeheartedly agree with this.
I have a friend who took her 3 kids to a character buffet in WDW a few months ago. All 3 kids are over the age of 10. She told the waitress that her kids were triplets...all age 9. So she paid the kid's price for all three kids. When she got home and told me this story, she was actually proud. She said that it was ridiculous to have to pay an adult price for her pre-teens. When I asked her why they ate there she said, "Well, because we love the restaurant and the characters and the food." Ugh.
Needless to say, we got into a bit of a debate. Here's the thing, for kids over nine you are paying for more than just the food. You're paying for the wait staff, the character interactions, the overhead associated with the operations of the restaurant, etc. I think my friend was completely rude to walk into that restaurant and proclaim that because she didn't think the set price was fair then she was going to set her own price.
If you can't afford to dine somewhere, or you think the pricing isn't fair...then don't eat there. It's Disney's restaurant, they get to set the price. And, you get to decide whether or not you want to eat there.
OP...this frustration isn't directed at you. I've just been frustrated about this whole incident since my friend told me about it. I think that openly lying about your child's age is tantamount to stealing. Just my opinion. In fact, I think that if your kid is 10 you should tell the wait staff honestly so they aren't left guessing.