A name for those who are born to a witch

Doesn't matter, if your writing supports the noun then all is good. Trivial questions support trivial results, amigo .

 

"Witchling" sounds okay to me. The ending "-ling" has a diminutive and gentle feel to me. It would be hard for me to think of anything big or dangerous being called "-ling".
The image I get is of 4-5-year-old children running around and laughing.

 

Witchling sounds fine to me as well.

You could play with different words, depending on who is speaking. If you have a group in your story hostile to witches, they might use "Witchbrood" or "Witchspawn" instead, whereas the witches (or those friendly to witches) might say witchling.

You might try looking for synonyms for offspring, see if that inspires some new ideas. I did that today after reading your post and came up with some I might like for a story of my own (if the need ever arises), like: Witchwhelp, Whelpwitch, Fledgewitch, Witchmite....heh. These are a tongue-full [sp?], and they have various connotations that might not be useful to you, but the idea inspired me.

 

Witchling works. So does Witchborn, Witchblood, Witchboy/Witchgirl depending on their bits, etc and so on.

 

Well, the obvious answer would be a child right? What others may call them might be different depending on who is affixing the label. 'Devil Child' might be a term that got used. But that might be over playing the question. Witchling is fine. Maybe you could make up a name, like Wuggles, as a way to refer to those who were not blessed with the challenges of being non-magical human types.

 

Witchkin is another that'd work.

 

Witchlet. Just joking. I'd probably go with Witchling, come to think of it.