I have always found this to be an interesting debate, and have traveled to WDW with children at 5 mos, 8 mos, 14 mos, 2.5 yr, 3, 3.5, 4 and 4.5. These were all trips of at least a week and all went off without a hitch. I can't see "depriving" my oldest just because she's got a baby brother. You just have to take it easy. I have three points I'd like to bring up that have been bothering me for some time. (Mostly due to prying in-laws wondering out loud if I'm crazy for wanting to got to WDW 2x a year)
First, where there are babies, there is crying. Everyone always says I've never seen more crying babies than at WDW. OK folks, babies cry, they cry when they are hungry, tired, messy (they also cry at home in their nice cozy cribs). Just because you pass a crying baby doesn't mean it's being tortured. I'm sure if you hung around long enough you would find it's needs attended to. Secondly, this whole thing about 'they're not going to remember anything'....huh? You don't think they'll remember a happy childhood and quality family time? Perhaps babies should be banished from ever going to sit on Santas lap, zoos, restaurants, carnivals, etc because they won't remember. All of these things are a learning experience for babies and frankly, my son is so much happier when we are out and about in a stimulating environment. Thirdly, they are basically free at WDW, so why not bring them, I mean cost really isn't an issue.
I'll get off my soap box now...ahhhh I feel so much better.
Now to the original poster...If I lived in Orlando, you can bet I would go to WDW with my daughter alone on occassion and have a wonderful time, but for most of us who live a distance away, thats not feasible. I just wouldn't feel right leaving a one year old with grandma for a week. I also agree that if the heat/sun index is dangerously high that baby needs to stay out of the mid day sun. I have always traveled during cooler periods. I thank you for bringing up the topic.