My family is two adults and three kids also. At first glance it can seem frustrating to find a place for larger families to stay, but there really are plenty of options at WDW. As you can see by clicking on the
In-Depth Planning Topics link for Larger Families on the WDW website, there are rooms for five in every price range.
In the value resorts, there are the Family Suites in the All Star Music resort. These rooms sleep up to six people and as an added bonus have a small kitchenette and two bathrooms. (The two bathroom thing is HUGE in my family of girls who need their quality mirror time in the morning.)
In the moderate category, you can stay in the cabins at Fort Wilderness. Here you have a full kitchen and access to plenty of outdoor space for the kids to burn off some energy. There are also rooms at Port Orleans Riverside that have trundle beds which allow a third child his or her own bed.
And all the deluxe rooms can accommodate a party of five in a regular room in two queen sized beds plus a daybed. The deluxe rooms also offer lots of square footage, which is great if you have strollers to store in the room as well as people.
Last but not least are the villa-style rooms at many of the deluxe resorts. There are villa rooms that can fit up to 8 people in apartment-like suites with full kitchens, washer/dryers, and more.
You can get pricing and availability for all these types of rooms by calling Disney reservations at 407-W-DISNEY.
Have a great trip!