This is causing a lot of confusion.
I am not a part of Duo Hindi team but I am a native Hindi speaker and I can say with absolute certainty that NO ONE can mark you wrong for using "hai" in a negative sentence. In fact, everyone around me uses "hai" in most of their negative sentences. Dropping "hai" in a negative sentence is quite rare although not incorrect.
Thanks, but this offers no clarity. First, if both variations are correct, that should be made clear to the learner rather than a haphazard appearance of both. I dropped "hai" in two of the exercises and was marked wrong.
Second, the learner should be offered some sense of the actual usage, not just that both are "correct." emrys29 asserts in the previous post that "Dropping "hai" in a negative sentence is quite rare..." I personally don't believe this is true at all. It contradicts authorities like Tej Bhatia and Rupert Snell. (If they are wrong, then by all means they should be corrected, but is the Duolingo team peers of them?) In any case, let us assume it is true. Then learners should be informed that the situation is rare, so they can prioritize doing what is actually most common. Be consistent or explain why it is inconsistent. Is it because previous prominent Hindi grammars are based in Delhi speech, for example? Are both deemed "correct" just because someone has heard someone say each of them? If that's the case, this lesson should be teaching "mere ko," which tons of people say.
I think because if it were a general statement ('children do blah' in English is implicitly - and supposedly - applies to all children) it would include 'hota', though I don't know exactly where that comes in a negative statement, I suppose before the hai, so last if it's dropped.
I can think of several meanings for this sentence. Can you tell me which ones are plausible translations for it, and which ones (if any) are clearly wrong? 1. Children (in general) do not eat apples. (I think this is the intended meaning of the sentence.) 2. There is one specific apple that the children do not eat. 3. Each of the children do not eat a single apple only (but they may eat more than one). 4. Each of the children do not eat multiple apples (but they may eat just a single one).