We spend a LOT of time in World Showcase. My favorite films, in order are:
China
France
America
Canada
But that's an adult with teenaged children's opinion.
The America film does have some animatronic figures (sort of like Hall of Presidents) that come out between parts of the film. That could hold the children's interest more than just a movie.
I like the China film the best because I'm always amazed at how varied China is. But there isn't much action in that movie, so the kids would probably get bored quickly (and it's standing only).
The Canadian film comes across the most dated to me, probably because it has a lot of people in it, and it's obvious it was filmed in the early 80s. The American film is mostly historical, and the other two films have way more scenery than people.
I'd suggest taking the films in at nap time, and doing only the films with seats. Maybe your little ones will catch a quick rest while you're off your feet.
I forgot to mention Norway has a short film also. It has seats (fairly uncomfortable, but seats). It's more a tourism film though. I've only seen it once, since I usually walk through after getting off Maelstrom. If you really want to see it, you can go through the exit. I wouldn't suggest Maelstrom with young kids. Those trolls are scary!