They don't ask who you are ordering for. How would they know know? And why would they care?
We did it everyday for lunch. I came to love my applesauce and grapes!
absolutely - but i don't know if you can do it on the dining plan. i would double check the rules on that, i think they are fairly strict, if you are using the dining plan.
(i don't know for sure because we've never used the dining plan.)
People split and share at table service restaurants all the time. No worries there. But if you are using the Disney Dining Plan, unless you pay for the kid's meal OOP (out of pocket) for the 10 year old, it will use one of the adult TS meal credits.
That's the only time you'd need to think carefully about buying kid's meals for kids 10+. If you're not on the dining plan, no worries there, either.