We're a family of 4, our children are 18 and 15. In looking at different savings passes that are available for the London attractions, it appears the majority opinion of posters in this forum is to not get the London Pass. The 2-for-1 pass from National Rail seems to be preferred. However, I'm noticing that many of the attractions we're interested in seeing offer "family tickets" that offer a pretty nice discount. St. Paul's, Shakespears Globe, Tower of London, and Westminster Abbey all have family tickets, and the Churchill War Museums would be free for our 15 year old. Does anyone know off hand if the 2-for-1 savings works out better for a family like ours compared to buying the various family ticket admissions?
I have not priced out the London attractions recently. They all have different definitions of family, but most include only two adults and your 18 year old will be an adult. Your 15 year old may even be too old for family tickets and child discounts. I doubt that family tickets will work for you. If you do qualify for family tickets, they will probably be more expensive than using the 2 for 1 discounts, I don't recall any attractions that were half off with family tickets. All you can do is price the attractions out yourself.
The family price is generally what it would cost for two adults and one child, so the second child gets in free. However, the child price is usually for 17 and under, so your 18 year old wouldn't qualify. Even if they did admit them as a child, you would still save more with the 2 for 1 tickets since both children would be free. I would go with the 2 for 1 deals and check out the family tickets for sites that aren't part of the 2 for 1 scheme.
I have looked into this extensively (and have the spreadsheet to prove it!), in general the cut off for a youth or child "concessions" is 5-15 or 5<15. Study the 2-1 pass opportunity carefully...
Right you are, I was overlooking the fact that our 18 year old wouldn't count as a child for purposes of the family ticket. Looks like Westminster Abbey would count an 18 year old as a child for purposes of their family ticket, but not the other places. Looks like the 2-for-1 passes will be the way to go.