Like dreamzpainter said, discounted tickets will end up costing you something like time out of your trip for a sales pitch. The one place that consistently gives a small discount on WDW tickets is AAA. Disney changed the whole ticket pricing structure in 2005 and when you buy a "base" ticket of the lowest price, it only entitles you to go to one park that day, which for your age children would be The Magic Kingdom. There is an additional charge to be able to access the various parks. This website has a good explanation of the complex ticketing system with prices and a lot of info and photos of the on-site accomodations. http://www.allears.net/
If you decide to Disney for only one day, an alternative for another day is the Orlando Science Center. It has attractions for children of all ages and is low key and hands-on. http://www.osc.org/
It’s off the topic but the Maryland Science Center in Baltimore is another place young kids enjoy.