One of the major tools used in PBL for kindergartens is mindmapping.

International Projects Uppsala

Mind maps can be used to help children see concepts and the relationships between them and externalize their ideas. They also help teachers to assess children's conceptual development and understanding, identify misconceptions, and facilitate learning by building new knowledge on old knowledge. In preschool education, direct instruction and modeling of mind map creation are needed in order for children to see their purpose and eventually create their own mind maps. Once familiar with the idea and the process, children can construct their own maps either individually or collaboratively.