Hi!
Well, let's see...the first thing I will tell you is to "go with the flow" on jet lag, if you can. When we adopted our son, I made the mistake of forcing myself onto local time (as I always did when traveling on business). But you really can't do that to a small child. So I was keeping myself up all day and he was keeping me up all night. NOT a good plan! I would suggest trying to arrive in the afternoon/evening, find somewhere to let your children run, then go to sleep when they do. They may be awake again at 2:00am, but at least all of you will have gotten some sleep. Then you ease into the local schedule.
As for keeping them occupied on the plane, it can be pretty hard if they don't sleep for at least part of the way. DVDs help. Little toys (particularly new surprises) help...but don't use anything you'd be too upset to lose...a dropped toy can disappear pretty quickly (for example, roll several rows away in turbulence when the seat belt sign is fastened). Walking up and down the aisle (or around the galley if they'll let you) helps. But a lot of it turns into sheer endurance if they don't sleep. Also, if your younger child won't have his/her own seat, you may want to get a Baby B'Air. I got ours on eBay. You can't use them during takeoff or landing, and I question the claims that they make your child a lot safer (it would take pretty severe turbulence before I can see much effect there), but a Baby B'Air sure saved my shoulders/arms on one long flight. Holding the full weight of a sleeping child (even a small child) on your lap for hours is torture on your upper back, because they're always pulling you in one awkward direction or another. The Baby B'Air helps support some of the weight, at least.
Just my $.02
B.