This requires more patience than anything else. Once you receive the quest, you'll see quite a few of the sprites. But don't start attacking just yet. Just stand there in front of the NPC for a bit and look around you.
You'll see several pairs of running sprites. And then, if you look close, you'll see a couple of single sprites, often lounging around on the ground.
Now watch to see the path that the running sprites take. And how long it takes them to complete a circuit.
NOW, look for a single sprite, and WAIT until any running pairs that path by him have gone by. Attack the single sprite. If you are ranged, pull them away from the path of the running pair. If you are melee, attack and then back up out of range of the running pair when they path back around.
The two lesser scamps each one summons when about 1/3 heath are very fragile. Don't worry about killing them. Kill your main target first. The two summoned scamps will die on their own seconds after you finish killing the main target. I often only managed to kill one of them before the other one died on its own.
But the point is that you'll see lots of sprites/scamps and -- if you're a typical WoW player -- you'll just start in on killing. That's a good way to die yourself.