Erin,
With so many good choices inside Epcot, there is no reason to leave the park for dinner. But if by "CMC" you meant Cape May, you really aren't going very far. It is maybe a 10-15 minute walk? So not a huge time commitment, especially since you are not waiting on a bus or boat.
As to dining INSIDE Epcot that might be a good dinner choice, I have several favorites.
Rose and Crown is an easy favorite, but I also like
Biergarten, for the festive dinnertime atmosphere.
Akershus is great, and very magical with a little girl.
Teppan Edo I like, though I think much of the fun is lost on most 2-year olds, so I would say no on that one. One other I would consider is the
San Angel Inn.
As to an ADR time, I would suggest that most meals take about 1 hour. I would schedule an ADR 1 hour 15 minutes before a show, at the very least. That should get you out in time to get a decent, if not premiere location to view the fireworks.
Have a magical (and delicious) vacation!