Ok, sorry. I'll try to clarify.
What we see in the books:
-Three Jackdaws as a human and as a golden dragon. He compares himself to a witcher (for the mutant issue), implying that he can't have children. We don't see any other dragon adopting human form as we don't see any more dragons besides a baby one.
-There is also (it is mentioned, doesn't appear directly) a she-dragon? dragoness? who was poisoned. She is who called Three Jackdaws for help in the first place. He did the job and took the dragoness' child. If he took the baby because the mother died or just as payment for the helping is not clear.
@Dona
While never directly confirmed, the implication of Three Jackdaws sterility, the fact that he had a baby dragon at the end of the story, and Saskia not being golden but claiming that she was his daughter, strongly suggest, in my opinion, that Saskia is actually that dragonling of Sword of Destiny.