"The child has a lot of hair."
Translation:Het kind heeft veel haar.
"kind" was said to be wrong and "kid" was suggested instead. And: Isn't "haar" and "haren" both correct as possible translations?
The first thing must be a typo, I hope you reported it. Regarding your question: in this case it can only be haar. The child has a lot of hairs would translate to Het kind heeft veel haren.
If , as you say, veel haren means a lot of hairs then why is 'she has long hair' zij heeft lange haren?
Because heel=really, very, and veel already means a lot. So "heel veel" is a reinforced expression, like "a whole lot". A simple "a lot", is just "veel".