We are headed to Disney in 19 days

and I have the same problem!
My dh, ds4 and ds2 are on the
free dining plan, so I ASSumed that all of us would be receiving the free meals. Once I began to call and make our ADRs, one of the CMs told me that ds2 is not in fact on the plan. I asked how that could be since all of the information that I had read on the DDP said that everyone booked into the same hotel room had to be on the same plan. That's correct, the CM told me, except that 2 and under are free. Well, I said if he's free, does he eat for free? Only off of your plate, said the CM. How is that supposed to work? asked I, mother of a child that eats more than his 4yo brother that is on the dining plan. Well, all children 2 and under eat free off of the plate of the adult. Pardon me while I vent - this has been extremely frustrating to resolve.

AGH!
After numerous calls and a variety of answers, it is clear to me that Disney is not quite sure how to handle this issue. Here are the conclusions that I have come to and the advice I've unearthed via my
travel agent and other DISers.
1. You can not purchase just the dining plan for your little one. I asked the same question and was told that I would need to purchas a park ticket for him if I wanted him on the plan.
2. Your child CAN eat free off of your plate.
3. Can you request a separate plate for your child to put the food on? That seems to depend on where you are eating. At a sit down restaurant, that will probably be fine. Buffets appear to be the trickiest as several people have reported being charged for a separate meal for that child. Be sure to advise your server/waiter that the child is under 3 and is eating off of your plate. Double check your receipt before you leave the restaurant to be sure that you haven't been overcharged.
4. CS meals will be fine, no one will be watching how you divide your meals up.
5. One mom on another board wrote that she brought a sippy cup for her younger child so that she could divide up the drinks between her kids. There are no drinks included for the under 3 crowd.
6. My travel agent suggested that when I am ordering, I just politely tell the servers that this child is 2 and will be dining for free. She said to specifically mention the age so the server is clear on why I should not be charged for an additional meal.
I hope that helps. When I go, I am just planning on needing to purchase at least a couple of meals/snacks for my son. Like I said, I don't think that Disney has a clear plan of how to deal with these little ones. At least the CMs I spoke with through ADR didn't!
Can't wait to read responses, especially from anyone that has done it before!