One does not simply gather up these NPCs and AoE them down. While they hit for a pathetic amount of damage, the danger with these sprites lies in their Shin Kick ability that stuns quite often and leaves them scampering off to throw more rocks at you. If you're a tank trying to AoE pull, forget it. Their low damage means low Vengeance, and chain stuns mean you can spend literally 10 minutes trying to chase em down if you pull too many at a time.
In essence, they're the bratty children throwing rocks from your front lawn you've always wanted to strangle, or even more aptly (as someone put it), the murlocs of Pandaria.
Edit: Forgot to note. One of the easier ways of dealing with this quest is simply picking off the Sprites as they're kicking braziers and starting fires. They gain a DoT that burns them down quite fast (burn, wretches, burn!) and simply tagging them at any percentage will count towards the quest objective. Helps to scream your favorite Ragnaros quote while doing so.
By fire, be purged!
Edit: As of a few days before this post, they hotfixed Sprites so that they no longer Shin Kick as much. May your bruised shins rejoice!