I'm a native English speaker in the US, and In my view all 6 sentences you listed are okay. Apparently, they were looking for answers that included the words "used to" and "not," and so his no. 2 is considered preferable to your no.
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AnonymousA word of advice: never confront the teacher like you did. Some people love to do this: point out correct answers on tests that are wrong or debatable, but this kind of thing does you no good. There have to be standards in an educational environment, and things can't be perfect, and so pointing out minor flaws like this is pointless.Dear Anonymous,
AlpheccaStarsBut the alternate "used to not" is found in everyday speech. Here are some sample quotes from the American Corpus:I used to not care about marriage until I fell in love.That used to not be OK with me, but now it is.I used to not follow through on things. She used to not wear dresses. She hated to wear dresses. They're coming back in Florida now, Ohio, Montana
Juliar FadillahSo would it be correct (acceptable) to answer this kind of question in an exam with "I used to not fly a kite when I was a little kid"?That would depend on the examiner's prejudices.
Juliar FadillahDear AlpheccaStars,So would it be correct (acceptable) to answer this kind of question in an exam with "I used to not fly a kite when I was a little kid"?If you had to give one correct answer, then stick with tradition.