If a budget is a consideration, try the Residence Inn, Sea World or The Convention Center.
A two bedroom suite, is the way to go. You will have two bathrooms, a kitchen, and the money you will save, just on a full breakfast, for seven people will be a $100 per day.
You will also have a place that the kids will be relaxed. Much better than a "Cramped", hotel room. Likewise, having meals, snacks, and drinks in your refrigerator will pay big savings for you.
Grand Lakes is by far the best of the Marriott properties in Orlando. It's connected to the Ritz Carlton which has an excellent spa. The rooms and common areas are also nice...especially the pool area with the lazy river feature.
The World Center is also nice, but quite large. If you need more space, the Vacation Club Villas are good. They also offer all kinds of activities for children and adults.
You may also want to also look at the Marriott Imperial Palms timeshare and Marriott Royal Palms timeshare. They are both right next to the Orlando World Center Marriott. The time shares have 2 bedroom 2 bath units with full kitchens. Sometimes when a Marriott timeshare is next to a Marriott resort the timeshare people can use the resort pool.