Is this correct?

[Rich7]

The model describes the process of a child learning its first (native) language.

This is an extract from a site on the page of antimoom.com.
under INPUT.

why its intead of his?

Thanks...

[Torsten]

Well,

From the grammatical point of view the word child is neutral (neither male nor female) which means you would have to use the personal pronoun it and the possessive adjective its. However, I prefer referring to a child as they so as to make sure the child can be a girl as well as a boy. Even better if you use the plural form children: Let's take a look at how children learn their mother tongue.

TOEIC listening, talks: Starting a new employee orientation program

[Rich7]

man, thaks god I found this site. Am I learning?
definitely yes...

[Swayam]

hello friends.

"The man WAS sustained injuries."
i know the above sentence is wrong because the correct word is HAD and not WAS, but how to technically explain that why it's wrong?
Please explain. Thanks :)