My children were born in the Outer Hebrides. It's not Welsh, it's Gaelic. They lived there until they were 6, 4, 2 and dd1 started school there, went to Croiligean (Gaelic nursery) and roinnigean Beag (creche for age 2-3) there.
When we moved to Glasgow, we'd researched the bilingualism thing enough that we continued - and now SGG (Sgoil Ghaidlig Glaschu - Glasgow Gaelic School) is the largest primary in Glasgow, they're building another school here and Edinburgh is now getting a dedicated Gaelic school too.
It's a bit political here - there's a lot of comment about the "Gaelic mafia" - those who don't let their dc speak anything else, and are very involved in school issues. But most folk are in it for the immense benefits of bilingual education, and kind of for the school culture in the motto "Da Canan, Da Chultar, iomadh cothron" which means "2 languages, 2 cultures, many opportunities".
I'm an English language teacher, but I really value the extra language my children learn. And the cultural advantages such as music, singing, sports that a bi-cultural school brings.