24-105 is probably the only lens you'll use in Disney. And I second all the advice here to concentrate on preserving the photograhic moments of your family as upposed to the scenery. For example, when my wife and I go to the zoo with our kids and grandkids, I'm usually the one a few steps away, or ahead, capturing the kiddos. I sneek in an occasional animal portrait but the memories I take away will be of the little ones. the 50mm will be perfect for those indoor shots of kids looking through windows.
The last time we all were at a zoo, we saw a group of togs (no kids) carrying around huge amounts of 1 series bodies, L lenses, and Gitzos. It was more than enough to generate serious tog envy and I'm sure they got some cool animial portraits -- but not of any little girls or boys looking at them
At disney, take the time to wait for the characters and get the kiddos obtaining signatures (by all means get them autograph books). Go to goofys kitchen at least once. spend the time at poohs corner and capture kids with Eyeore, etc. let them play on the fire engine.... the 24-105 will be perfect.