We went in September during
free dining with a 2-yr-old and he did not have a set of credits, but had no problem eating during the week.
At TS restaurants he just ate off the adults' plates - at a couple of places they even brought him his own mashed potatoes (a favorite thing) or other side dishes. At buffet places we just got him his own plate and there is no charge since he is under three. All of them brought him his own milk/water cup and once brought him some ice cream for dessert even though he didn't have a kid's meal.
At CS restaurants he ate from our stuff, and he ate his older brother's kids-meal grapes more than once (the 4-yr-old older brother doesn't like grapes). A couple of times we purchased oop for him (i.e., a kids pack when older brother was starving and adults were sharing) but that's very minimal. We also carried in cracker packs and fruit bits and juice boxes and stuff for him in his diaper bag. Being that young we were already going to have to have a stroller anyway, so carrying this stuff was no issue.
We were there for eight days and we spent maybe $15 total on food for him.
Maybe. Much less than the $75 to buy him a one-day ticket so he could have his own credits.
Also, since Disney is the ultimate in recordkeeping where their visitors are concerned, aging him to 3 now would have resulted in prematurely aging him to 10 from 9 later - which opens up a whole new set of higher charges on a future trip for the sake of saving $15 now.