My dd1 started school in the same building as her peers (wheyey it was a big p1, there were 5!) though she was the only one who went into GMU.
We moved to Glasgow when she was going into p2, dh into last year of Sgoil Araich and dd2 had a year to go (where we lived in Harris she'd have had 2 afternoons a week in Rionneagan Beag - wee stars- that was a playgroup for age 2-3).
I couldn't put a p2, totally immersed in GM, into a O2 in English medium, she'd sink as she only read Gaelic! So on our move we were really lucky to get her a place at the Gaelic bunsgoil in Glasgow. Ds went to the nursery, followed by dd2.
Now I've got a p5, p6 and s1 (now in Ardsgoil) kids who are totally fluent (I realised recently I only know if they're using bad langua ge!!) despite the fact I speak limited, taught by their school, and dh no, ghaidhlig, my 3 dc are totally fluent. Recently we were at a wedding and the grooms mum is a native speaker. My dc chatted away all night - apparently it totally made her day!! They speak it pretty much exclusively (except to me and dh) on our holidays to our house in the hebrides. Very popular with our elderly neighbour!
They might never use it. But I can see how it's helping my dd1 with French, and biligualism also has been shown to boost maths and music.
As I've said before - our kids are very musical. Dd1 (13) plays Accordion and piano. Ds (11) plays piano, drums and chanter (for pipes). Dd2 (9) plays fiddle and piano. I'm planning on having a ceilidh band!!)
Also, dd1 who has now done a couple of years of French at school can actually hold a (fairly simple) reasonable conversation with a girl at church who recently arrived from the Congo. She speaks little English, so dd1's ability in French is helping her fit in!!