Our family relocated when we were little because my dad got a job at the university. There were 7 of us kids, and our mom too! We all adjusted differently. I was the oldest. At 13 I got a circle of friends, learned the language, and would have stayed longer, even though I left friends back home.
The rest of the kids connected at different levels. My sister has lived in Mexico since, and speaks Spanish. I think most of the kids learned some Spanish, but don't practice any more. One brother began to learn to read in Spanish, and had a tough time learning to read in English when we returned.
My mom understands some Spanish, but doesn't really speak it. She used to read the paper to our maid. She understood, but couldn't read. Mom could read but not understand.
We made wonderful Dominican friends and it's sad that it is so difficult to keep in touch - or even find them after such a long time. I just hope they feel as fondly towards us as we do towards them
We returned after the first year, mostly because the kids were so homesick.
Would I do it again? Yup! That's why we moved to Japan during 2000 for my husband's job. We were able to give the opportunity to our kids. Maybe it would have been different if i didn't _know_ it was do-able. Would I still do it again? Yup!
Good luck in whatever you choose to do.