In a small bowl, combine the sugar and cinnamon. Set aside.
Pour the pretzel bites into your slow cooker. Drizzle with melted butter and vanilla extract, then toss to coat evenly.
Sprinkle the cinnamon sugar mixture over the pretzels and stir gently to coat all pieces.
Cover and cook on LOW for 2 hours, stirring every 30 minutes to prevent sticking and ensure even coating.
Spread the coated pretzels on parchment paper to cool slightly before serving. Store leftovers in an airtight container (if there are any!).