While I don't know anything about this particular package or its insurance, I can tell you this about
travel insurance:
It's usually a sucker bet; that is, it's heavily stacked in favor of the insurer (Disney) and it's unlikely to pay you -- especially if you're young and healthy.
Some people are worried about the war or terrorism (myself included), but war and acts of God (i.e. a flood) are usually not covered by insurance. So don't buy insurance because of political concerns.
If you're going to buy travel insurance, look around for the best price -- another company will almost certainly beat Disney's rate. It's kind of like the car dealerships and interest rates: sure, they can finance your car right then and there, but you'll pay a higher rate than you would at the credit union.
Before you decide to buy or not to buy, you need to know more information:
What cancellation policy do you have without insurance? Chances are you can get most of your money back even if you cancel fairly close to the trip. This means that the insurance would only be useful if you had a catastrophe right before the trip (which probably isn't likely).
What does it pay if you use it? Most travel insurance doesn't return your money; it allows you to re-book for a later date (usually within a year or so), and it doesn't give you 100% of what you've paid.
My advice is find out more about this specific policy, weigh its benefits against your family's needs, then make your decision.