Add whipping cream, sweetened condensed milk, whole milk, and vanilla to crock pot. Whisk.
Stir in milk chocolate chips.
Cover crock pot and cook on low for about 2 hours, stirring about every 15 minutes. When chocolate chips have fully melted and mixture is combined you may want to reduce your crock pot to the 'warm' setting.
Prior to serving whisk mixture vigorously or stir with an immersion blender to froth.
Serve plain or with a variety of toppings such as marshmallows, whipped cream, crushed candy canes, M&M's, and more.