Mallorca (Alcudia).
10 days came in at just under 3 grand for self catering in a complex with two pools right on beach and flights (not includign food, though.
Plus points:
Short flight time
Uber child-friendly place, almost exclusively visited by families
Most of the hotels have pretty great kid's clubs and entertainment for the children at night (ours had a kid's club running from 9am-6pm, mini disco and games from 8-9.30pm and then showed a kid's film with popcorn in the hotel lounge from 9.30-11pm (staffed)
The beach is lovely - sandy and shallow, warm waters.
Transport is good - regular bus services going anywhere you'd want to go.
There's a water park in Alcudia.
Pollensa is slightly more up market (just slightly!) and about 20 min bus ride away.
There is a gorgeous national park - Albufera, I think it's called - 20 min drive away, with cycle routes, more rugged beaches and landscape, watersports etc
Palma is an hour or so by bus and is much more cosmpolitan if you want a bit of culture.
Tourists are a good mix of Europeans, not just Brits. Loads of Germans, Scandis and Irish, so don't have that Brits abroad thing you get in lots pf touristy parts of Spain.
It's not an 'adult' resort, so no noisy nightlife or boozed up teens.
Low points:
It ain't highbrow! 
Food is very samey everywhere you go.
The Euro exchange rate these days means food isn't cheap. We spent a lot on eating out - more than we'd have liked to.