Drizzle the inside of two 12-ounce glasses with chocolate syrup. Place in freezer until ready to use.
Place marshmallows on a small baking sheet. Broil 4 to 5 inches from the top until toasted and golden brown, about 1 minute. Cool completely. Set aside 2 marshmallows.
Meanwhile, spread marshmallow creme on the rim of the cold glasses. Sprinkle with 2 tablespoons crushed graham crackers.
Combine remaining 8 toasted marshmallows, ice cream, and half-and-half in a blender. Cover and blend until smooth. Divide between prepared glasses. Top with whipped cream, additional chocolate syrup and graham crackers, the reserved marshmallows, chocolate, and sprinkles, if desired.