I see several aspects here:

• Perl and graphics: Is this about creating graphical user interfaces (GUI) - or about creating pictures and animations? For GUI, the choice is, well, difficult. For a somewhat narrower scope, SDL Perl comes with a book Writing Games in Perl (a bit stale, though). If it's about creating beautiful images, you could start with an app like harmonograph (based on Wx) and work from there (but see the third item below).
• to be used in more up to date contexts: That would make it difficult for Tk. While the widget demo provided with the library is very helpful, it shows a style which is very idiomatic to Perl - and to a somehow old-fashioned Perl style in particular. Also, Perl/Tk apps look a bit "old". On the plus side, to my knowledge it is the only toolkit which allows to define events on individual canvas items.
• An important aspect of is to get it running in the environment which your son wants to use, and unfortunately this isn't always trivial. So, I would be tempted to recommend WxPerl, but unfortunately it doesn't install cleanly from CPAN these days. For example, for Windows and Strawberry Perl there's the open Bug #129768; applying the patch suggested by Kai-Uwe Eckhardt in that bug report makes installation work and tests pass.