I think you should appreciate the incredible deal you're getting - it is FREE, and yet, you want to lie and manipulate the system to get your child more expensive free things.
IMO, this goes way overboard. I would MAYBE see people thinking about considering their child an 'adult' as long as they're paying the extra $30 a day for that option. But for free...that is totally taking advantage.
Okay - your child doesn't like a lot of the child options...MANY kids fall into that category, not just yours. If you plan well, you can find some CS options that are not mac n cheese or chicken nuggets...and then do buffets for TS if you want. Then, your child can have a huge variety of child and adult foods every day. And, if you still end up at a location where your child doesn't want any of the options...use a couple snack credits to get him something OR pay OOP for a couple items - it is FREE, it will still be a heck of a deal even if you spend a few dollars here and there on some items.
It is because of people maniuplating and finding loopholes and ways to lie for their own benefit that WDW likely even instituted changes to the children's menus to begin with...
Obviously if you're going to do it - people on this board aren't going to change your mind. But if you're truly looking for opinions, I think it is a horrible, no-integrity idea.