WARNING!!!

If at all possible - do not take a 4 year old on a 27 hour international journey. Especially one who you don't really know, and haven't spent more than a few days with, and don't share a common language with, and who has never worn shoes let-alone a seatbelt and who spends most of the time removing both from his body. Especially don't attempt to undertake such a journey with a child who spits at you and yells "imbee" (I refuse) loudly all through an overnight flight (I thought it was a good plan so he'd sleep) and also if possible not with a child who has stomach parasites so must use the washroom every half hour, or with a child who can squeeze under the security bars at Frankfurt airport that sport a sign saying "Entrance Strictly Forbidden", in
English and in German (Eintritt Verboten!!) which sounds scarier.
And if you can avoid planes with the screen on the back of the seat in front which the child will poke really hard for 5 or 6 hours causing the passenger in front to freak out, I'd advise you to do so. I'm just sayin'.