There is one in Tewkesbury called Croft Farm water park . It is quite busy, and a half way house between a large all singing and dancing site, and one with not much facilities. They have a small lake for watersports, own boats, hire boats and canoes.
I went there with my husband and 5 year old a couple of years ago. It was quite child friendly for 5 up, I would say. It is a mix of statics and tourers.
http://www.ukcampsite.co.uk/sites/details.asp?revid=1811
Feezee
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Took a break like everyone over covid, flogged the caravan and got a campervan!
Hoburne Cotswolds, near the Waterparks just outside Cirencester is an option.
They have a swimming pool indoor and outdoor, tennis courts, playground, small soft play, bar with entertainment if thats your thing. Also fishing on site.
------------- 2015 sites booked so far: Cotswold Farm Park, Ninham IOW, still some more to book
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.