Really there are so many possibilities
A bit trite but there is the classic Maker faire Maker Day Robot.
http://www.thingiverse.com/thing:40212/#files
and the 3D hubs Marvin Key Chain
http://www.thingiverse.com/thing:215703
How are your design skills. You could use 123D to make a simple key fob with the name of the school mascot. or find a 3d file of the animal resembling the school mascot.
You want to get real crazy get a list of the kids names (first name or nickname only) and make custom key fobs with there names KISS.
Hope this helps
tin
Soliddoodle 4 stock w glass bed------Folger Tech Prusa 2020 upgraded to and titan /aero extruder mirror bed
FT5 with titan/ E3D Aero------MP mini select w glass bed
MP Utimate maker pro-W bondtech extruder
Marlin/Repetier Host/ Slic3r and Cura