T.,
Relax! Two hours won't be bad. First, tell them in great detail what is going to happen. Pack surprise bags that contain something that will interest them for a bit. Bring snacks, drinks, a couple favorite books, paper and writing items, little cars, stuffed animals, toy airplanes, a couple cloth napkins (can be used as a doll blanket or used to clean up spills), a couple little dinosaurs. If packaged each in their own bag, it can be a SURPRISE each time they are getting restless. See if they can meet the captain when the embark. Tell them how much fun it is to take off, look out the windows, fly above the clouds. Take pictures of them in the plane, out the window. Trace the route with them on the map in the magazine. Ask them to imagine the birds that can see them. The 2-year-old might fall asleep, which would help. Make it an adventure, like a field trip. Let them each carry a little carry-on that they pack with treasured items (Mom supervised and approved).
I've traveled by myself with first my son and then with both my sons clear across the nation with one change of plane stop in the middle, several times. Last summer when we did this, they were ages 2 1/2 and nearly 5, so I can relate.
Overall, just try to keep a happy mood, and try to make it fun.
To purchase tickets, I scan the web for the best deals. Places like hotwire and priceline can be helpful, but don't forget to visit the individual carriers' websites for deals.
Best wishes (and I know you'll be fine),
K.