Yes, WL has a small store area. The baby care centers in the parks also sell those things. You can get a few types of baby foods and diapers, but the prices are pretty high.
There are several options--renting a car onsite for one day, using a town car to get to the Lodge and having a free grocery stop, use netgrocer or send a package to yourself, or use one of the grocery delivery services that are talked about on these boards.
If you take the things you'll need it will give you more souvenir room on the way back!