Question: I've been taught that a *child* is gender-neutral noun. But in the textbook on linguistics I've been reading, the noun is used as feminine. For example, a sentence in the book goes like this:

> 
> The child must also learn many aspects of grammar from her specific linguistic environment.
> 
> 
> 

Is there an explanation for the use of the pronoun *her* instead of *its*?

Answer: 
From historic perspective, `it` used to be an appropriate pronoun for a child.

<http://archive.boston.com/bostonglobe/ideas/articles/2008/09/28/a_girl_called_it/>

This is similar to other Germanic languages that have grammatical gender (which has degenerated in English except rare cases like ship-she), like German "das Kind" or Dutch "het kind".

Modern connotation of the neutral pronoun in American English seems to have changed as other responses note.
Child is not gender neutral, but it is gender normative. In modern English it is gender neutral, but it depends upon its use and more importantly it derives from kilþei a Gothic word for Womb. It entered Old English with a female gender moniker and retained it only until the onset of Modern English. Arguably, Child/Cild is thus feminine in gender reference especially within given contexts referencing pregnancy. While it has been made neuter through over usage. 

This reflects the gender bias but gender normative nature of the word "guys". While masculine in nature and in its original usage, it has also gained a neutral usage.