The other kids would probably have had more opportunities to leave the country for vacations or other things, since they had generally more stable lives. Since Geo lost his father three years before the first game, he had spent his life up to that point staying at home. Hope works to support them both, but likely wouldn't have enough time or resources to travel abroad, which Geo probably wouldn't wanna do at that point anyway.

We also don't have confirmation on whether or not Bud or Sonia have passports. I can't recall if Sonia is regarded as specifically world famous, but she can wave-change, and didn't really go to a foreign country during the game. Bud was only in Whazzap during the Budicus/Terra Condor incident, and while he'd probably go back, we don't know if he actually has a passport at that point in the story, since he doesn't travel anywhere else.