CP is great for a 6 year old as you won’t need to pay for any activities if he’s happy pottering around and exploring the beach and all the parks. Longeat is fab with the land train too! The 4 days will fly by and two will be changeover days (arrivals and departures). The pool is mostly warm in the wave pool (perfectly safe for 6 year olds) and weirdly the outside pool as it’s warm as long as shoulder under. The kiddie bits might feel cold to him as the water is shallow and kids run around out of the water. Could he have a wetsuit or similar. Honestly though even with 1-2 swims and the rest exploring/walking/train/park/beach the time will go fast. Take some Cook meals and cook in to save a bit of money but still have a treat! Or the dine in menu for takeaways was really good.
also with CP like others have said - it’s chilled and slow. So take some toys and dvds and chill in the lodge too. Often ducks and deer pass the lodges.
someone mentioned stag and hens - I’ve never seen this so might have been a one off. Never had any issue with noise or boisterous behaviour. Most people are respectful and I thought they actively discouraged big groups?
it’s pricy yes - but worth it and familiar for us too.
we also like the bit with the shops and sometimes just go for a walk, few parks, up to get an ice cream and coffee, then slow walk or train back for lunch. Depends where lodge is of course but often there’s a destination of sort with an ice cream!
hope you find something suitable.
sorry just thought - for the pool you can take towels and things in to pool area. So you could take warm things for a break and cuddle. There’s cafe in there too!! Then warm up, snack and rest and back in again if he wants. There’s cabanas you can hire - little huts with tv in pool area.