Photoshop Elements is available for less. Doesn't have all the bells and whistles but has the basics for learning the program. If your 12 yo has any inclination to progress, I'd stick with this software path as opposed to other "equivalent" programs.
ebay example (no affiliation):
Adobe Photoshop Elements 8 #1 Selling Consumer Photo-Editing Software- For Mac | eBay
MHO,
Sherwood