Near Barcelona. We're fully immersed and avoid the expat community, to be honest.
We've got beach 5 minutes walk away, mountains 20 minutes by car.
Kids can attend "school" from the calendar year they turn 3 (so a child born October 2023 can start school this september, although be quite young). That's P3. P3-P5 school is optional, at age 6 they start 1st year of primary with proper classes. I've no idea what the equivalent is in the UK. There's also kindergarten for under-3s but they're not flexible, eg two afternoons a week or something. Basically as soon as they each the age for P3, everyone signs up cos it's 9-4.30/5 with 2 and half hours for lunch! And it's free. You pay to eat a hot meal at the school, or collect them to eat at home and return at 3pm. No packed lunches.
Teenage DD is currently in third year at secondary. She went to the feeder school from primary, so with 90% of her classmates. Secondary timetable is 8-2.30 with a half hour break at 11. Bar the usual idiots, she's enjoying her time at secondary, there's been minimal bullying or other issues. It's a state school with three classes of 30 per age/year.
After-school classes were plentiful at primary, although we just headed yo the local park for an hour or two yo let kids run around and socialise more, often parents would celebrate birthdays there and load picnic tables with food, easy to organise. State schools don't have uniforms, only private schools up to 2nd of secondary (so at 13).
We've found parents are the same the world over - some nice, some idiots, some rude, some hilarious, warm and friendly! I'm still in close contact with a handful and our kids are still friends.
It's a hot country for the most part, so outdoor activities are the norm all year round. It's been 16°c since Saturday and that's the Catalan coast, not Andalusia.
Oh, depending where you move to, you'll be learning Spanish + another language. I had rudimentary Spanish but now I've got C1 Catalan as well! Kids pick up languages crazily easy!
It's been great raising our dd here.