I can also recommend Bose's QC15 noise-cancelling headphones, but trust me -- the earplugs are a lot less expensive!
Seriously, with kids, the best thing you can do is set an example and hope they sometime follow your lead. Beyond that, try to keep them as comfortable as best you can.
It helps if they've taken local flights before, so that they don't feel the excitement of a first-time airplane flight - keeping them up for the whole thing. If that's not the case, just accept that they're going to be excited and their time clocks are going to be whacked out. (Actually, flying from London to Orlando during the daytime, excitement keeping you awake can be a good thing. It's the flight back that can be a bear.)
Exude as much calmness as you can. Try to apply your normal day/night routine to the destination time zone as soon as you get to the airport and during the flight. Change into jammies at the destination's bedtime and into day clothes at the destination's morning. But be ready with snacks and juice when tummies grumble and the kids get cranky.
If they see you calm and happy, you've got a chance that they'll be calm and happy as well. If they see you angry and stressed, then you've got no shot at an enjoyable flight.
Good luck.
What a movie geek I am.
By 5pm I had arrived at Universal Orlando, and at 6pm I was on The Hulk.
To this day, I still cannot believe how quick and easy it was to A) get through customs and bag claim at MCO; B) check in to the Royal Pacific and find my room etc.; and C) redeem my special unlimited pass tickets at the IOA front desk.
Some of you might it horrendous that I went straight to IOA after a 8hr flight from the UK, but it was this pleasant experience that has made me come back again in June 2011. Let's hope it goes just as smoothly this time!
P.S. on night 1 I stayed until closing time, 10pm. The following morning I had to be up early to make use of my voucher for a free breakfast at The Three Broomsticks at WWoHP, so I entered IOA at 7am. I didn't leave until closing time again, 10PM.
On day 3, I was very ill with sunstroke, exhaustion, and blisters on my feet, so I came home from IOA after a few hours and spent the rest of the day in bed. :(
On the way home, I do exactly the same. I know I won't sleep on an overnight flight but I try hard. I usually reach home at about 10am following 17 hours of travel. I NEVER go to sleep. Instead, I power on until around 8pm when I call it a day and crash out. I'm usually fine the next day. In fact, I started a new job the day after a trip on one occasion. Its mind over matter in my view.
Since, as you say, most jetlag is due to exhaustion, my approach is to sleep as much as possible regardless of local time. Most Americans go abroad for too short a time to adapt to local time anyway. I just can't trick myself to sleep when my brain doesn't want to sleep.
This leads to touring sites at odd times, but it's less stressful than worrying about jetlag all the time. Some travelers obsess over it, even when they have no business or meetings to attend to! Relax.
When flying to LHR or AMS, there are some wonderful "pod hotels" inside the terminal where you can pay per hour and sleep or shower after an uncomfortable flight. Four hours at "Yotel" in Heathrow's terminal 4 costs 26 pounds and feels like you've given yourself an upgrade.