This paper presents a co-design toolkit, Storytelling Shapes, that enables children to tell personal stories using various wooden shapes. Starting from these stories, designers can engage in a conversation about children's needs and wishes. The toolkit was tested and improved based on a pilot study and two co-design sessions with 16 children aged 6 to 11. After introducing the toolkit and discussing its iterative development, the paper concludes with a set of guidelines for using Storytelling Shapes in co-design activities with children.