I was of the understanding that all kids in Wales were taught Welsh as part of the curriculum.
I think it depended on the school. And North West Wales is a LOT more Welsh speaking than the rest.
I went to a very Welsh school where we were taught English as a lesson. Everything else, dinosaurs, Romans, history, science, geography, maths etc was all done natively in Welsh until the final years when we got a new teacher that wasn’t a fluent Welsh speaker.
The secondary school then had separate streams for Welsh / Bilingual / English but I don’t think many kids went into the English stream it was just there to cater to those that couldn’t speak Welsh. My parents were adamant that I was going into the Bilingual stream which would have made me the only 1 in the entire primary school going into it 😂 but we moved to England days before I was due to start due to my dad’s work moving,
It was pretty cool as I genuinely couldn’t tell the difference between Welsh and English , we’d get a book to read and my parents / grandparents would ask which language it was and I’d have to go back and check because even if I’d told them the title I’d have automatically translated it into English to tell them even if it wasn’t. Disappointingly picking up a 3rd / 4th language isn’t as easy, at least not learning it via the curriculum, maybe I’d have picked one up if I’d lived somewhere.