Inkscape is an open source vector graphics tool that is similar to Adobe Illustrator.
It is a powerful tool that is used by professional artists but I have used it with great success with kids as young as 4th graders.
I have used Inkscape in my Digital Design program in Los Altos School district in 4th and 5th grades across all 7 schools for 2 years. I have also used it for logo design with my CSTEM students last year. Approximately 2000 students have learned Inkscape in my classes and many of them still remember their Bears project or Blobs project.
Here are some tutorials based on my lessons.