Vicki,
Early March is our usual week so I have some experience here. The weather should be great with daily highs in the 75 - 85 range and it's the third lowest precipitation month, we've had one rainy day at WDW in about 35 days there over the years. Treat yourself to a copy of Bob Sehlinger's Unofficial Guide to WDW, any decent bookstore should have it. You've got plenty of time to read the descriptions of the rides and attractions and decide what your 'must do' things are. Make a list. Since you're on property you qualify for early entry to the parks on certain days and to stay 3 hrs later on others. Use this, particularly the early morning time. Get there 20 mins before early entry, use FastPass and you'll get many of the major attractions in before lines get long. This is the start of the busy season, but crowds are what I would call Moderate. You're kids are not too young, so they might really like World Showcase at Epcot. Our strategy is to get to the Early Entry park early, do the attractions until crowds bulid, usually about 1 pm, then we hop to Epcot, every day. Epcot swallows crowds and never seems too crowded.
For each park, have a loose plan as to what you want to see/do and in what order, but be flexible, it's not a job. If something not on your agenda appeals to you, do it! Don't miss Illuminations, Fantasmic or Spectromagic and decide in advance which nights you want to see them. YOU WON'T DO IT ALL! Don't even try. This is a physically demanding vacation. If your party can't walk 5 miles a day, every day for a week, get in shape. I eat and drink like there's no tomorrow at WDW and come home lighter than when I go.
In general, bring your sunscreen, batteries, film, OTC medicines and first aid stuff because they're outrageously expensive there. Bring multiple pairs of comfortable walking shoes. Finally, frequent these boards, these folks will make you a Disney Pro in no time. We're there from March 2 - 12. If you're in World Showcase some mid-afternoon, peek into the Rose&Crown and see if these characters are there.
Bill From PA