Monica,
These are great
Disney Dining Plan questions!
Buying Credits for Your 1-Year Old?
You don't have to buy credits for your 1-year old. Children under 3 are able to eat from their parent's plate at buffet and family style restaurants (and it is encouraged). At a la carte restaurants you can just buy her what you need. There is no plan available for those under-3 children.
Speaking from personal experience, this is GREAT! We saved so much money and still felt like our little one got plenty to eat.
How Many Credits Do You Get?
You get 3 meals and 2 snacks, per person, per night spent in the resort. So you are staying 5 nights, which means each adult will get 15 adult meal credits and 10 snack credits for the trip. And the child will get 15 child meal credits and 10 snack credits for the trip.
Refilling Your Cup?
You only can re-fill your resort mug at your resort hotel. So if you are staying in the Polynesian, you can fill it up at Captain Cook's. But you CANNOT fill it up at the Grand Floridian Resort, or the Magic Kingdom, or Downtown Disney. Just in Captain Cook's.
I hope that this helps? Feel free to write me back with any follow-up questions!
Have a magical (and delicious) vacation!