A sweet blackberry syrup mellows mouth-puckering limes in an intensely fruity (and kid-friendly) drink.
Cooks' note:
To make blackberry syrup, heat 1/4 cup blackberry jam with 1 tablespoon water in a small saucepan over moderately low heat, stirring, until jam is dissolved. Pour mixture through a fine-mesh sieve into a small bowl, pressing on and then discarding solids. Syrup keeps, covered and chilled, 1 week.