We're heading the other direction - and smaller time difference, but when we've gone to the UK with small children, I've found they adjust better than my DH does.
For your scenario, at Disney, I'd plan the complete first day to be resort only - if up for more, go ahead, but just plan to swim, walk, go to DTD maybe. Enjoy the day, let the kiddos sleep as needed, BUT shorten naps to an hour. Up for at least 3 hours before another nap. Try to get them to stay up until at least 6PM - later gives a later wake up the next day (IME) before you let them sleep for more than an hour.
Aim for a nice hearty, early (buffet maybe) breakfast the next day - RD, and heading back to the resort in the afternoon for a nap and a swim - for us, our 7 yr old can have up to 2 hours of nap time and still go to bed IF she also gets to and runs/swims or something. So after a nap - get out and get them busy free playing - at a playground or pool. Then bedtime as per usual.
The 3rd day will be ready for whatever your Disney time happens to be.
Our Disney time is typically RD until 3PM, then naps (for the adults
) swim, dinner, swim, bed by about 10PM. We find this works well for us.