I was googling recipes this afternoon and I stumbles across this one. It sounds too yummy not to share.

Dairy-Free Coconut Hot Chocolate

adapted from In the Kitchen with A Good Appetite by Melissa Clark

2 tablespoons unsweetened cocoa powder

15 ounces (1 can) coconut milk

1/4 cup dark brown sugar

1 ounce bittersweet dairy free chocolate, chopped

1 teaspoon vanilla extract

1. Bring 1/3 cup of water to a boil and pour it into a mug or small bowl. Whisk in the cocoa powder until totally dissolved and set aside.

2. In a small saucepan bring the coconut milk, brown sugar and salt to a low simmer until completely dissolved. Then whisk in the cocoa and chopped chocolate until completely dissolved. Stir in the vanilla and serve hot.
I'd chuck a couple of marshmallows in there too

I guess that if they could tolerate tiny amounts of dairy you could use a regular 85% chocolate instead of a dairy free one because it is a pretty small amount.