I am a grandmother. My first WDW experience with children along was when my two DGDs were 7 months and almost 5. My DD asked if I would go with her and "help with the kids". Her DH was willing to pay my way! (If the truth be known, he probably made this offer just so he wouldn't have to go...LOL) Of course I said, "YES"! We flew down, rented a car, and stayed at CBR. Most days I decided to do my own thing with the baby in Epcot, my favorite park. I took the car as it was easier to transport the stroller and all the baby stuff. And my DD and DGD4, took the bus to MK and we'd meet back at the resort at dinner time. Taking a 7 month old was perfect! She could sit up in the stroller, but still couldn't walk, so there was never a problem keeping an eye on her. She was old enough to be excited at the various things she saw, but young enough not to care where I took her. A perfect combo for baby and Granny! I've been to WDW many other times with DH and on trips with older grandkids, but I have to admit that one was pretty special. So if you are asking about the age of a child for YOUR trip, then I'd say go as soon as you are comfortable traveling with a baby. (I'd choose a cooler time of year).