It's a long flight but I'd have to recommend San Diego. We were there last year and it was fab - we don't have kids but we reckoned it'd be perfect if we did have them and if the number of Irish accents we heard around the place is anything to go by, it is very popular with Irish people young and old!! There's the Zoo, Seaworld etc for organised days out and then fabulous weather, beaches and parks for lazier days. It's freakishly neat and clean and tidy as well which is presumably a selling point for people with little ones!!