I also recall there being 2 autograph books - a small one which would fit in a small bag but was not that distinguished, and the larger one, which was decorated with Disney princesses on the cover and throughout.
It had spaces to hold photographs on the inside and lots of room for autographs, which the characters filled up, often with personal messages for the girls.
They were for sale at the souvenir stalls just through the railway tunnels and are well worth getting, even if they cost a bit more than elsewhere.
Get them as soon as you arrive (you will sse characters everywhere) and put the child's name inside the cover as many characters check this first, and then write a personal greeting with correct spelling etc.