You must learn a special skill to tame Lesser Dragonkin. For pets of this family other than cloud serpents, the skill is taught by the tome, How to Train a Dragonkin. This is awarded by Kaestrasz in Valdrakken at renown level 23 with the Valdrakken Accord. It is only awarded to hunter characters with the appropriate renown, you cannot achieve the renown on a non-hunter alt.
Location & Notes:
Located in Stonetalon Peak, Stonetalon Mountains. Hostile to both factions. This fey darter appears only sporadically in the area, and is often killed by hostile NPCs. It may take you a while to find one.