I'm going on Friday also with my two kiddos and I am taking the double. My oldest is almost 5 and my son is 2 1/2. My daughter may end up walking the whole time, but I want to keep my options open and if she does end up walking, then I'll have more room for all of the "stuff" (we're bringing lunch) and won't have to shove it all down into the basket underneath.
I'll do just about anything to head whining off at the pass, so I would play it safe and bring the double. Hope you have fun! We're looking forward to it. I noticed you're in Houston...are you going for the Zoo Boo? My daughter loved it when we went a couple of years ago. Hope you enjoy your day!
I should mention that mine is a sit n stand, so my daughter hops on and off as she wants to. I fear now, though, that they will fight over who gets to stand in the back. Guess we'll see how it goes!