If you learn a language as a child then stop using it, does it lie dormant?

[StMary]

We are considering a move to the French speaking part of Switzerland. We are British, DC only speak English as do we (other than rusty school French).

We don't know how long we'll be there but say we had 5 years there (DC would be 5 and 2.5 when we arrive) I'm guessing they'd be pretty fluent in French (they'll go to local schools), but would lose a lot/all of it if we then move back to the UK, or do languages lie dormant in the brain and can be reactivated with less effort than starting from scratch?

Obviously it's all hypothetical but it would be nice to keep it up so perhaps a French speaking au pair and some lessons would help.

Just would be a shame to go through the pain process of learning it just to lose it again......

Different experiences obviously. My nieces lived in French-speaking Switzerland and went to kindergarten there till they were 3 and 5. American mum, Swiss German dad. So they had three languages fairly fluently. Then moved to Austria, German everything apart from English speaking mum and au pair. They're completely fluent in English and German, but the older one gets terrible grades in French at secondary school nad even her pronunciation is poor. You'd never guess she was once fluent!

I think it does kind of lie dormant and so would be a lot easier to pick up again when you return.

You'd probably still speak a lot of English at home though right?

This research suggests that, to an extent, it does lie dormant:

www.bbc.co.uk/news/science-environment-38653906