Asking purely out of interest, cos I'm a languages geek and a nosy bugger 
If your DC are growing up in a country where their mother tongue isn't the main language spoken 'out and about', what were their experiences of picking it up?
DH and I are English speakers living in Sweden. I speak basic, jolty conversation Swedish and DH knows a little bit. I'm a SAHM and often go with DD to playgroup so she hears Swedish for a couple of hours at least three times a week, plus in shops etc.
She seems to realise in some way that she often hears something different to what she hears at home, and can say a few Swedish words that we have 'imported' into our day to day English. If I throw a few Swedish sentences at her she seems to get the gist, especially if they contain a familiar sounding word eg Klappa händerna.
She can also (sometimes, if she's in the mood!) say some of the words from the Swedish songs we sing at playgroup.
I am so intrigued to know what she makes of it all! What goes on in her head, what will happen next, what does she think when I speak Swedish to her for fun.
No 'point' to this thread as I say, just interested to hear about others' experiences as I find it a fascinating process to watch as a parent!