The real Aesop of this game is "Homemade costumes are inherently better than store-bought ones"
Dorian's magic is the reason the costumes allow the kids to fight back against monsters.He's incredibly powerful, much like his sister, but since he's too afraid to face her, he invests his power in the three heroes instead, trusting their imagination and pluckiness will pull them through. Which it does.
Wren and Reynold are from a family of wizards.They're the ones who are empowering their costumes. Their family recently moved away from a place where magic is expected.