What personalised actually means here
Most personalised children's books are one fixed story with a name dropped into the blanks. Two children get the same adventure with different labels on it. This works the other way round. Before the story exists you fill in a panel about the child it is for: their name, the animal they love, the things they are into, and, if you want, one real memory from their life. That panel is not decoration applied at the end. It replaces the generic character the engine would otherwise invent, so the plot itself grows around a child who likes dinosaurs and has a cat called Mimi rather than around a placeholder. You can add a dedication that sits at the front of the book the way it does in a bought one. Every field except the switch that turns the panel on is optional, and a name on its own already changes the story. Leave the boy or girl choice empty and the writing simply uses the child's name wherever a pronoun would otherwise go, which is the right answer more often than a form usually allows.