Give your kids the jumbo marshmallows and some plastic knives and tell them to "sculpt" a heart out of each marshmallow.
Meanwhile, chop up the chocolate into small pieces and place in a large mixing bowl.
Heat the milk over medium-low heat until scalding (don't let it boil).
Add the sugar and stir until dissolved.
Remove from heat and add vanilla.
Pour about one third of the milk over the chocolate and whisk until the chocolate is melted.
Slowly adding the remaining milk, whisking constantly, until all of the milk is incorporated.
Divide the hot chocolate into 4 mugs and top with the heart-shaped marshmallows.