The only reason for hoppers in your case is the fact you're staying at a Epcot resort, we stay at BC and we love the walk through Epcot to the monorail, it allows us to have a beer or two and maybe get a character in, we are in Epcot everyday.
That being said if I was paying for my own trip(I am very blessed to have my mom still pay for DD and I) and my hubby was coming with me I would figure out a way to do it without hoppers. With kids that young you can leave mid day take a long nap and return to the same park.
How long does it take to walk through Epcot to the monorail? Then take the mono rail to MK? Is the bus faster?
We're paying for my parents also and I would hate to pay the extra and them be too tired to go back out at night. Can we add them to certain tickets but not all of them if we're all on the same package?