Red soft drink concentrate like Kool-Aid.
Here's the recipe (which includes a non-alcoholic version):
2 ounces 1/4 cup vodka
1/2 ounce 1 tablespoon Grand Marnier or Cointreau
3/4 ounce 1 tablespoon + 1 1/2 teaspoons WHITE cranberry juice cocktail, see notes
1 small bottle red color liquid sugar-free soft drink concentrate like Capri Sun, Kool Aid, etc.
Red rim sugar if desired
Fill a cocktail shaker with ice then add vodka, liqueur, white cranberry juice and squeeze of lime wedge. Before disposing, use rest of the lime wedge to wet the rim of a martini glass. Turn the rim in the red rim sugar.
Shake the cocktail shaker for about 30 seconds until well chilled. Strain carefully into the prepared glass. Add one drop of red beverage concentrate to resemble “vampire blood.” Garnish with open vampire fangs.
To make this drink family-friendly, just leave out the alcohol and serve a cranberry cocktail.