I grew up in the home of an expat with kids (my dad was the expat and I was the kid.)

I'd say expat kids have their challenges, but not worse than other kids, just different. They'll struggle with their cultural identity and with fitting in, but they'll probably be independent thinkers and will adapt easily to new environments. That was my experience, anyway.

Should probably mention that I went to english speaking schools the whole time though, so the language barrier wasn't such a big deal.