I can honestly tell you to rest up for the trip. You could be there two weeks and still not see everything there is to see. I am heading back there this year for a family Disney wedding, and I can say I am not looking forward to it. I find the experience fucking exhausting compared to most other vacations.
I do not know how people who have children keep up for a week or two. Many we've met before while down there come in and stay for literally two weeks. I guess that actually does give them some days in the middle so they are not rushing here, and rushing there. Maybe that helps.
I've always stayed on property, and it's frankly worth it. I can only imagine the hassles of being off property. Going to Disney World versus Disney Land (Ca.) are two different monsters. The World will kick your fucking ass.