Hi Bethany,
I think you are wise to realize that Epcot is tough to cover in one day! It is actually two parks in one.
With your family, I would visit a few areas in Future World and then tour the countries. In Future World, Spaceship Earth, Living Seas and Living with the Land can be enjoyed by everyone. Test Track, Soarin' and Mission: SPACE have restrictions and someone will need to use the Rider Swap to watch the baby and maybe the five year old.
As for the countries, each one has something unique and special. I encourage you to start at Mexico and tour around the world until you reach the United Kingdom and Rose and Crown. There are activities for your five year old at each country at the
Kidcot Fun Stops.
You also have the fun of the
International Food & Wine Festival to enjoy around the World Showcase.
As for lunch, I would eat at Electric Umbrella prior to heading over to World Showcase. You could also eat at
Sunshine Seasons in the Land which is my personal favorite because of the variety of food. Or eat in a country.
Wishing you a magical vacation!
Beth