I'm sure we had a thread on this once but I can't find it so thought I'd start a new one. This may be old news to some.
DS went to the London Eye when he was off school recently because they were moving (therefore not as crowded as usual!). It cost a grand total of £5.75 for him and a carer! She went free and I think £5.75 is just the price of a child ticket. Well worth it.