So, sometimes the creators of these books conspire up some interesting, and sometimes naughty, things for the mum and dads out there.
One example that is well-known is from the Biff, Chip and Kipper books. The books are a UK teaching tool for young kids learning to read, but they have also become known for their Easter eggs seemingly thrown in their pages - purely for the parents benefit.
Now twitter user Ed Brody has found a new little gem.
Twitter were quick to come up with ideas for what was happening in the top left corner of the book.
Plus, twitter users were quick to post their own findings in other children's books. Enjoy!