Dragonspawn have shown up more than once.
The first time anyone fought Madame Voodoo she summoned a half dozen of them using a “Gate” spell.
The Dragon Orion brought a small army of them with him to assault the nation of Irkusska.
Nominally, the Dragonspawn are part of a larger faction called the Legion of Everblight. The Dragon “Everblight” having founded said faction. The PCs have seen very little of the rest of Everblight’s Legion save his spawn.