We rate Butlins for value. The price includes the pool (nice and warm, range of slides suitable for tots up to adults, splash area, rapids) plus soft play, fair rides, playparks, pavilion shows. Then there's the extras, such as bowling, indoor golf, arcades, circus. We stay in the hotel, as its a higher standard of accommodation. However, it's noisy and busy and non stop fun for kids, so might not be what you want.
Landal might be another option? They have lovely sites, mostly in the Netherlands, which are comparable to centre parcs. They have some sites in the UK, usually set in nature, but less 'going on'. Much better value than CP.
As PP have mentioned, Centre Parcs in Europe is often better value, even after channel crossing, but is a bit more travelling, depending on where you are in the UK.
Or just find an AirBnB or cottage or glamping site in a preferred location?
Or look at Eurocamp, Yelloh or other holiday park places? I went to north France in May half term to Domaine du Drancourt, only 1.5hours from Calais. Lovely rural setting, near to pretty towns, coast, etc. But I live in the South, so not too far for me.