P.P.
Hi. My husband and I went to visit my family in Kenya over Christmas with our 11 month son (he is now 15 months old). The time difference is 8 hours and the trip was not as bad as we thought. I let my son sleep when he needed to and his jet-lag resolved itself within 5-7 days. The first three days were hard because he was up for most of the night/morning. We then started shortening his daytime naps and he slowly corrected his sleep pattern.
My son has NEVER slept through the night and he still wakes up 3-4 times a night to nurse... so I was not hopeful for a quick solution to the jet-lag (my expectations were already really low). I have to emphasize that all children are different and your son may do wonderfully.
I have read that it takes a day for every hour of time difference for sleep to match the new time-zone.
Your trip sounds amazing. How many wonderful memories will you have traveling to Mongolia with your son? I hope you have a wonderful trip.