Some websites that offer free labeled diagrams of plant cells for free are KBTeachers, TeacherVision and Internet4Classrooms. These sites have educational resources for children of different ages on plant cells and animal cells. The plant cell diagrams can be printed out, and there are diagrams that teachers can use to test students.
The KBTeachers website has both an unlabeled and labeled diagram that can be printed out at the same time. This website has many other free plant-related resources for teachers such as worksheets on photosynthesis, plant anatomy and the function of different plant parts.
One of the many resources offered by TeacherVision is a free printout that is a very simple version of the plant cell, and it is suitable for younger students.
At the Internet4Classrooms site, there are a variety of diagrams available for free that include a comparison between the plant and animal cells, plant cell worksheets and PowerPoint presentations that teachers can use in their classrooms. The plant and animal comparison handout for students contains all the different parts of both these cell types. The site also provides labeled diagrams that give definitions of each part of plant cells. Some of the different plant cell parts defined are the cytoplasm, nucleus, chloroplasts, ribosomes and Golgi apparatus.