Hi Daniel:
Disney provides
various methods of complimentary transportation, such as buses, monorails, and boats, throughout Walt Disney World to take its Resort guests to Parks, Resorts, and other Walt Disney World destinations. My family, which includes two boys ages 5 and 4, always relies on Disney transportation to get around Disney property. We never rent a car. On occasion, such as an early morning dining reservation, we will take a taxi, but otherwise, we have always been satisfied with Disney's transportation system.
Buses are generally scheduled to depart every twenty minutes or so, but we find they often arrive earlier, though on occasion, you could end up waiting a bit longer for a bus. I find that the Port Orleans Resorts have decent transportation that it's not worth renting a car. However, I'm not sure of your budget. If your budget allows for a car rental, then you may find that having a car with you is worth the extra minutes it saves you in transportation time. However, for my family, we generally find the expense not worth it.
Enjoy your vacation.