The only caveat about OKW is that only three of the 49 buildings have elevators. If you can't get a first floor studio, then you might have to carry the infant and the stroller up to the second or third floor. Not to mention that after a long day at the Parks, grandparents can get cranky about walking up one or two flights of stairs.
The CMs at OKW are very good at trying to accommodate requests for a first floor villa. But sometimes one isn't available and you'll have to make [do] with what is available.
Good luck!