Hi Christy:
There is no doubt that your family will have a blast with your current plan. But as a Disney fanatic with so many memories of the Magic Kingdom dating back to when I was six years-old, I can't imagine not dropping by the
Magic Kingdom during a five-day trip. The Park is large and diverse in
rides and attractions, parades, shows, characters, and atmosphere, especially for six and nine year-olds.
I normally advise against too much Park hopping for families with younger children as it's easy to lose steam during a Park "transfer," but if your family can muster the energy, I recommend stopping by the Magic Kingdom. Perhaps splitting the day between Animal Kingdom or one of the Water Parks.
Again, there is no doubt that your trip will be amazing without stopping by the Magic Kingdom. But as a purist, I strongly recommend seeing if you can find the time to stop by.
Enjoy your vacation.