Families are paying high entrance fees and facing long queues at some of Britain's favourite theme parks, according to a Which? magazine report.
Researchers had long waits for a ride on Alton Towers' Nemesis
A family ticket for two adults and two young children visiting Alton Towers can cost up to £89, the survey found.
Researchers for the consumer magazine also visited Drayton Manor, Chessington World of Adventures, Thorpe Park, Flamingoland and Legoland last year.
Alton Towers said the price was value for money for a family day out.
Researchers said that - while the parks were a lot of fun for both children and adults - child prices were "particularly unfair".
They found most of the parks charged children over 12 the full adult fare, except Legoland - although its child ticket was the most expensive at £24.
The survey also found thrill-seekers suffered the longest queues, often waiting more than an hour for a ride on Nemesis at Alton Towers or the Vampire rollercoaster at Chessington World of Adventures.
The magazine said long queues were the parks' biggest drawback, with opportunities missed of keeping people occupied during the dull wait for popular rides.
Legoland - adult £34, under-15 £24
Alton Towers - adult £32, under-12 £22
Thorpe Park - adult £32, under-12 £20
Chessington World of Adventures - adult £29, under-12 £19
Drayton Manor - adult £20.95, under-12 £16.95
Flamingoland - all ages £20
It also criticised a number of the parks for selling only fast food, and having no nutritious choices.
Lorna Cowan, editor of Holiday Which?, said: "The whole family will have a great day out at a theme park, but if you've got teenagers, a family of four could end up spending almost £130 - and that's just to get in."
She advised families to book ahead to ensure a good deal.
A spokeswoman for the Tussauds Group which owns Alton Towers, Thorpe Park and Chessington World of Adventures, said it was "disappointed" with the report's findings.
She said many visitors were able to get cheaper tickets online or through special price deals.
Queues for some of the big rides were part of the experience to help build a sense of anticipation, and healthy food options had been introduced since the researchers' visit last year, she added.
Legoland, meanwhile, said child prices were higher than elsewhere because children were able to experience everything in the park - whereas in other parks there may be, for example, height restrictions on some rides.
The attractions - Alton Towers and Drayton Manor in Staffordshire, Chessington World of Adventures and Thorpe Park in Surrey, Flamingoland in North Yorkshire and Legoland in Windsor - were selected as being the six most visited by market researchers Mintel.