Help the kids pour the pomegranate juice into ice cube trays and freeze overnight. You'll want 12 to 16 cubes.
Make a simple syrup: Combine the sugar and 1/2 cup water in a small saucepan and cook over medium heat, stirring, until the sugar dissolves. Remove from heat and let cool. Refrigerate until ready to use.
Stir together the lemon juice, simple syrup, and 2 cups water in a pitcher.
Have the kids drop 3 or 4 pomegranate ice cubes into each of 4 glasses. Divide the lemonade among the glasses. Top off each glass with 1/4 cup seltzer water.