Oh wow - I think a lot of this was covered in other threads - might be worth doing a search to find it but anyhow, I came here to Spain 12+ years ago with littl uns. The state schools are great, very friendly especially the smaller ones, its the secondary schools that can get a bit ahiry - ideal to move to private for those 4 years if you can afford it. If yours go to Spanish school then private spnaish schools are way cheaper than international ones.
The sports are very behind, no playing fields etc, but many after school sports not too expensive and held at the local athletics gournds usually. My lad went to the football which is taken very seriously here from all ages - twice a week triaing then games. Now plays rugby.
Daughter did badminton, then running for the town!
Kids settled straight away, got the language quickly but then they were younger - most schools have non spanish europeans and put on special calsses to help them catch up. I feel the system is very good academically and keeps on top of the kids with testing. They never pined for the UK (not home now)
Went for state as hated the thought of paying for it and glad I did that although both went to private secondary schools as not enough encouragement to do well. Daughter now studying last year Bachillerato heading for Uni in Science subjects and will do well, aslo speaks frenach and some german too as well as fluent english and spanish.
Yes glad I made the move - never looked back and never regretted it despite the tough times and there have been loads!
Good luck!