Hi Sudesh!
I just went to Disney last month with my 2-year old son and 6-year old daughter, and even at the "Funnest Place on Earth," these kids still need rest time don't they?
Something that really saved my wife and I (mentally at least-smile) was renting a double stroller. Even though our daughter was technically too old to need a stroller, when she started to get tired, the stroller provided a perfect retreat. The strollers at Disney were large enough to where our daughter could lean back and fall asleep comfortably if needed. Or, if you're lucky enough to have them both tired at the same time, they'll sleep leaning on one another without falling out (It also makes for a perfect picture-Timeless moments)...
Most of the parks have benches strategically placed throughout, so the family could get a breather at one of them if needed.
Or, what our family would do, is stop at a table service or quick service restaurant and eat slowly, to give us time to re-charge our batteries.
If you'll be staying at a resort, in worst case scenario: leave the park, get a nap at the resort, and return to the park later. There was the rare occasion where the only solution for our son was to take him out of the environment. But mostly we were able to "tough" it out.
Good luck on your vacation!