In about a month's time, I will be flying from Phoenix to Detroit with a three-year-old and a 13-month-old. Alone. The three-year-old will have her own seat. The infant will ride on my lap. First off, am I crazy? Secondly, what is the best battle strategy to get everyone from one gate to the other alive?
First of all, you're not crazy for traveling alone with your children. People do it all the time, and have done it, if contemporary animated features are to be believed, since the Ice Age. On the other hand, flying from Phoenix to Detroit has kind of an out-of-the-frying-pan ring to it, as though you were deliberately trying to hit North America's least-appealing cities in one trip. How about a stopover in Dayton, too?
Basically, when it comes to non-baby kids on a plane, all you can do is give the appearance of making an effort. You're not really worried about getting the kids there safely. You're not even worried about whether or not they behave. You're really worried about the shame of appearing, in public, to be a bad parent. This is understandable, because people are quick to judge kids on airplanes.
So, since you've obviously decided to take the Southwest Airlines death march, I would definitely advise you to focus on the three-year-old. The infant will either eat or sleep or scream because its ears are exploding. The three-year-old's needs are more complicated and its chances to annoy more diverse. Anyone who complains about a crying baby on an airplane has obviously never had a baby and will receive karmic payback by one day being forced to parent the world's most colicky child. Anyone who complains about an out-of-control three-year-old has a little more justification, because three-year-olds can, at times, be modified for public consumption.
Load up on snacks and toys and coloring books and lots and lots of videos. If you don't yet have a cheap portable video player, I would recommend one highly. I don't care if it's against your principles. If you have little kids, and intend to travel without bothering others, than you need to keep them mollified. If your child is somehow easily mollified without video, then please donate that child to an institute, where its behavior can be studied for the benefit of future generations of terrified parents.