Actually I can guess how it works.
No, you can’t. Can you understand that any business, particularly one like Chessington with huge investment in plant and machinery, salaries to pay etc. needs to bring in £Xm per year just to break even? Including covering the cost of investment in new attractions, like its Sea Life centre, over a particular period of time consistent with the business case for building it.
The business looks at how it might bring in the £Xm, based on how many people it expects to get through the doors and the demographic mix of those people.
The point is, the same number of people have to deliver at least £X million of revenue between them. The only question is how the prices are structured; if one group pays less, another group must pay more.
It can charge the same for everyone, or apply differential pricing, including offers on cereal packets, but it still needs to raise £X million in revenue. So it decides what pricing structure would be most attractive to its customers. They have decided that a flat price for anyone 3 and above works best.
Charging £30 for 3+ on peak means families who are taking several older children at a weekend are also stung for smaller children.
Alternatively, having the flat price structure means that the over twelves pay less than they would have to if younger children got in half price. So it’s actually better for families with teenagers. That is clearly more attractive to the park’s target market. The family with a mix of older and younger children would pay the same even if young kids got in for less because, once more, if one age group are charged less, another age group will have to be charged more.