Scoop out and measure 10 cups watermelon pulp. Puree watermelon and sugar in batches in blender until smooth.
Push puree through mesh strainer into a large bowl. Cover and freeze until puree is slushy but not solid, about 3 hours.
Remove from freezer, stir in chocolate chips. Place 24 3oz disposable cups in 2 shallow baking pans (spoon puree into cups to within 1/2" of rim). Place pans in freezer until puree is solid but not rick hard, about 2 hours.
spread softened sherbet on top of each portion of puree so that it comes up to edge of cup. smooth top off with the edge of a butter knife. Cover each cup with plastic wrap and cut small slit in center. Insert popsicle stick into each cup so it reaches the bottom. Freeze until solid, about 6 hours and up to 2 days.
To unmold: Let pops sit at room temperature for about 1 minute. then gently pull out from cups. Or you can peel away the cups from the pops.