Not exactly the same, but I thought I'd let you know of my experience. My son usually does not eat child type food. We feed him "adult" type food and does not like chicken fingers, hot dogs etc. So we decided to ask if we can purchase the adult plan for him, even though he was only 6 and MS had told me that fine, we will just put him down as 9 for the purpose of the DDP. And that was that.
I also believe that if you feel you would like the DDP for your two year old, you can just ask them to do the same. But, just for info, we have AP's and use points for the reservations so we don't purchase tickets packages.
Otherwise, my suggestion would be to just pay out of pocket and buy him what you want. So it's more flexible, you can just add it to your bill and they will charge you for the extra items. Since you are not required to get the DDP, give yourself some flexibility and just order things for him. There may be a time where he may not like any of the Child's menu choices and if you get DDP for him, you'll have no choice.
Just a suggestion.