What are the numbers on the left-hand page in the Search-and-Find Books?
In the images there are various animals and objects connected to the country/place you're looking at which need to be found. The numbers beneath the objects on the left-hand side of the page tell you how many of each object there is hidden in the picture. For example, 4 x Cheese, 15 x Baguettes etc.
The hidden objects have nothing to do with the secret message. They're just an added element of entertainment within the book, alongside the hunt for the number on each page which will reveal the secret message.