We've booked with Travelgan Holiday Farm. I have high hopes as it's marketed as very family friendly. We are only 2 & twins but I think they have somewhere that sleeps 6 or you could hire 2 places at the same time. Very reasonably prices IMO.
Ayr caravan park is the closest to St Ives. Its quite a steep walk from St Ives itself esp if you are pushing a buggy!! But the view is amazing and the caravans are fantastic. Outside St Ives is John Fowler. We stayed there about 5 years ago and vowed never again! It was quite expensive for what it was and the "chalet" we stayed in was basic at best. But it may have improved and the children loved it. There was entertainment in the evening which although we didn't really want to go to seeing our childrens faces actually made the evenings great. The pool was also very basic but ok for younger children. There is also St Ives Holiday Park which is in Hayle just outside St Ives it is close to the sand dunes so location is good. We have not stayed there so cannot really comment although friends have and once again its a bit like Butlins on a smaller scale but their children loved it and made lots of friends. Ayr gets booked up really early as the site is a prime location.