Another good time is in January after the first week until mid-February. Summers tend to be too crowded and extremely hot. It is very taxing on anyone, but especially so on a small child. Holiday periods are very crowded and make pushing a stroller very difficult. Long attraction lines lead to restlessness and limit the amount of attractions that can be experienced.
Spring Break is very crowded and warm.
Early October thru early November sports great weather and low crowds. All the Disney hotels are great and go out of their way to make sure you have a great trip. These resorts offer extra amenities that can aid in the care of an infant. The Wilderness Cabins in Fort Wilderness are extremely good, because they are very quiet and sedate. Your child will be able to rest peaceably without hearing rolling suitcases and running children outside your door.