Since you know your son better than we do, then how do you calm him down at home? When you need him to sit still for a haircut, dentist appointment, church service, etc... what do you do then? My DS was about his age when he arrived in our family and although he didn't speak English, he was able to obey when I told him to sit down or to be quiet, and he had lots and lots of issues at the time. You have some time before your adventure, right? How about practicing airplane trip with him and making it a game, so he knows what you expect of his behaviour when you travel?
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My Countdown Counting down to: Food and Wine Festival, Here I Come! 131 days, 4 hours, 56 minutes
My Previous Trips WDW Nov 1987, offsite
WDW-April 2007, AS-Movies
WDW-Dec. 2007, Contemporary
WDW-Jan. 2009, Caribbean Beach
WDW-April 2009, AS-Music Family Suites
WDW-Dec. 2009, Port Orleans French Quarter
WDW-May 2010, Boardwalk Inn
WDW-Nov. 2010, Animal Kingdom Lodge
WDW-Jan. 2011, Port Orleans Riverside/Polynesian
WDW-Oct. 2011, Pop Century
WDW - Jan. 2012, Wilderness Lodge
WDW - Jan. 2013, Art of Animation and Yacht Club