Our family of four includes two teenage girls, ages 14 and 15. It seems a bargain to buy family tickets at the attractions that offer them (e.g. Tower of London). Other attractions (such as the London Eye) offer Child prices for kids 15 and under. However, the 15 year old is very tall and looks older than her age. Does anyone know what proof of age is required for these places (if any)? I don't want to carry our passports around. I did order "Oyster Photocards" for the girls -- we'll be picking these up at Victoria station when we arrive in May. Would those show their age and be acceptable?