You may want to try the GIMP it is free! Take a look at
The GIMP is the GNU Image Manipulation Program. It is a freely
distributed piece of software for such tasks as photo retouching,
image composition and image authoring. It works on many operating
systems, in many languages.
This is the official web site of the GIMP, and contains information
about downloading, installing, using, and enhancing it. This site also
serves as a distribution point for the latest releases. We try to
provide as much information about the GIMP community and related
projects as possible.
If you want to go with commercial software I have been using Photoshop
Elements and would recommend it over Photoshop for middle school