"Let's not get into cultural bias here."

I have no idea what that means or what it applies to. Sorry, but you seem to be in the deep end of some pool, on your own. To spell out the concepts:

"kid" is young person.

"child" would be a relationship label.

30-years old would be Child, but not Kid, such as "Adult child." But all of us have met 30-year old kids. I rest my case.

I have no idea why someone would bring nationalities into this.