We have taken our 2 boys at a similar age to yours. You know your kids better than anyone else, but for us it worked fine to stay all day, every day. The main reason for not taking a break is that we go to WDW fairly infrequently (for these boards) - about once every 5 or 6 years. It seems an unwise use of my money to not take advantage of the parks while we're there. It would be nice to say "Oh just skip that attraction, we'll see it when we're back in December". Unfortunately, we don't have that luxury.
Here's another hint. I strongly concur with the advice of a nice sit-down meal to break up the day. But we do it at lunch, because it's a little cheaper than dinner. Eat a late lunch, and then just grab a snack around dinner. YMMV.
Steve in Omaha