Add the grenadine to a highball glass and then fill it with ice.
Top with lemon-lime soda.
Optional: garnish with a cherry. Enjoy immediately.
Notes
Grenadine is a brightly colored nonalcoholic pomegranate syrup that’s available in most grocery stores near the mixers! If you don’t have any grenadine on hand, just swap it for maraschino cherry juice!
Lemon-lime soda gives the cocktail great effervesce and sweetness. You could use club soda or sparkling water if you prefer but keep in mind they won’t be quite as sweet.