Upvote:1
One activity could be: you choose in turn a thing, an animal or a person. As soon as one see that, his or her points that out to others and awards one point. First one to 10 points wins. Of course you should choose neither things too trivial, nor too rare, but preferably typical of those places. You could play as a team, too: for example parents vs children or males vs females.
Upvote:2
Tablets, tablets, tablets! Load 'em up with videos, games and apps before you leave, and they'll be quiet little zombies mesmerized by the glow of the screen for hours on end. Works particularly well if they're not usually allowed to spent a lot of time playing with them.
A few caveats:
At the luxury end of the spectrum, you may not even need to bring your own: Asian long-distance buses these days can come equipped with airplane-style AVOD systems loaded with movies, TV shows etc, and the price difference between normal bus and luxury bus can be $10. (Random example: Transtar First Class, between Singapore and various points in Malaysia.) Fare for kids will be limited and not necessarily in the right languages, but odds are you'll find at least the odd Disney/Pixar flick in there.
Wifi is also increasingly common, although it's usually just a tethered phone or something and wholly inadequate for eg. video streaming.
Charge up your tablets before you go and turn them on airplane mode once on board, otherwise the batteries can die pretty quickly. (Some higher-end trains and buses have sockets for charging though.)
For the sake of your fellow passangers, bring headphones, please.
You didn't specify whereabouts in Asia you're travelling, but on narrow tracks and rough roads you'll get sick staring at a tablet pretty fast. Even the older Japanese bullet trains can vibrate enough to make some people queasy.