I could have written some of your thread, OP - I'm British, have travelled lots, now live abroad, have small kids ... except I don't have the faintest intention of moving back to the U.K.
I'm in Spain (sounds like you may be too) and the lifestyle with young children is just SO much better imo. Great weather most of the year, hardly ever rains, tons of parks, playgrounds, outdoor activities for kids. Plus they are genuinely welcomed just about everywhere, in any bar, cafe, restaurant. Every time I sit on a terrace with a 3 euro glass of wine watching my kids play in the perfectly clean and well-maintained playground while the other customers smile indulgently at their shrieks of laughter, I think I wouldn't go back if you paid me.
I love that I can combine city living with being outdoors a lot. That combo is hard to achieve in the U.K. unless you are really tolerant of the cold. I lived in Edinburgh a long time, and it's a beautiful city but oh god, the weather.
Schools here are a big plus for me too. My kids start infant school at 3, and I think it's amazing they will grow up bilingual. Provision for learning second languages in the U.K. is terrible - by secondary school you've missed the ideal window to learn another language. On the other hand, my kids will have English lessons 5x a week here, and most schools have a bilingual programme with at least some subjects taught in English as they get older.
Of course Spain has its cons - the bureaucracy is mental, lower salaries and higher taxes (but that pays off in much better public services). But I think the pros if you have a young family far outweigh them. I miss my friends and family in the U.K. but I don't miss the country at all.
I'd much rather live here and visit there, and I can't see that changing any time soon.
One question, OP - if you did go back and regret it, can you reverse that decision? It's so much harder to relocate to Europe from the U.K. now.