I've been traveling with my DD for a while now and have found that the mid day nap is a necessity. Before we instituted the break DD would pass out in the stroller around 1, and sleep for a good hour. Since she was out cold there was very little DW and I could do except wait her DD to wake. So now, we open the park. have a light breakfast, and then make our way around the park till about 1 have Lunch and then catch a bus back to CS or CB, and cool off either at the Pool, or take a nap in the room. After a few hours of recharging, we change clothes and head back into the parks. This strategy is esp important when the park closes after midnight and DD wants to stay till the Kiss goodnight. I know that you will easily loose an hour in travel time plus the break time. But with everyone recharging in their own way it makes for a much more enjoyable trip.
What ever you decide make sure that you are not pushing yourself or your family too hard. I know that a WDW vaca can be a bit pricey, but if members of your family are exhausted from running non-stop you're far less likely to enjoy all that the Parks have to offer.
Good luck.