Depending on how little your children are, we try to have a "down" day every other day. We usually do a full day at a park, (open till close), take a day off to relax, do another day at a different park, take a day off to relax...etc.
The kids really don't mind, since they can find enough to do with swimming, biking etc... and we go to Downtown Disney to shop on one or two of those "off" days. So we are never at a loss for things to do.
We go with the one-day pass, not the park hopper, so that may change things for you.
We just find that with 3 little ones (5, 8, and 9) that they are exhausted after 1 full day, that the day to recover before we do it again works great for us!
Good Luck, and have a great time!