Both my daughter's biological clock love to take their sweet time adjusting to new timezones. It's a torturous ordeal for me, especially if they're fully awake and starving in the middle of the night in Tokyo, because it's lunchtime back home in New York.
Jet lag is hard enough for grownups to get over, and practically impossible for kids. If the time difference is 6 or more hours, your kids may never adjust to the local time by the end of your week-long vacation (although they'll come close to it). The beginning of the trip is obviously the hardest, as by the end of it, they'll be closer to being adjusted to the local time. But how do you make the best of it?
Having traveled many times with my girls to other countries, I've learned that the best way for them to get over their jetlag, is to let them get their full sleep. In my experience, trying to manipulate their sleeping schedule makes for a very cranky and stubborn child. I've had meltdowns happen in the middle of a museum tour that sucked the enthusiasm for exploring right out of me.
Anyways, to set expectations straight, this means your days exploring a new city will be limited. Pushing them around in a stroller may work for short naps, but for them to get full sleep, you'll likely be back in your AirBnB. Instead of exploring for 8 hours a day, you'll get a good 3 or 4, although if you're in Spain, well, you might be able to make it back out again for dinner at 11pm!
So, I'll say it again, the best way to deal with your child's jetlag is to let them get their full sleep.
If they normally sleep 12 hours, then give them the full 12 hours. When they want to nap, let them nap their normal duration.
The catch is this, while they're up, try to keep them up for an hour or two longer (if in Asia) or shorter (if in Europe) with each passing day, until they're close enough to the local time. Keep your expectations realistic though, this can take an entire week or more, depending on how big the time difference.
So if they're in Japan lets say, and are up at 1 am the first night, they may go down for a nap at 5am, then back up at 7am all the way until around noon or later. By day 4, they'll be up at 4am, down for a nap at 9am, then back up at 11am all the way until 4 or 5pm, which is getting closer to the local time.
Hopefully this advice helps you on your next international trip.
Keep on traveling! And if you have any personal tips or stories, please email me at firstname.lastname@example.org
Thanks for reading.