I need the word/phrase in Chinese/Mandarin/Japanese of 'troublesome child' or a version of child with strong negative connotations/intonation.

Perhaps a word like punk comes close.

you've come to the right place, I've got enough animes and manga magazines to give you a japanese translation of the word punk. What I know is very basic so I can't give you a full phrase. Kono Yatsu is what you're looking for

Any specific relation to a sex or age, or is it more of a general phrase?

it mean punk

So it just means punk, with Japanese you have to be sure there is no particular requirements, ie sex etc, with a word.

Thanks.

no problems a helpful tip next time you are looking for a word in japanese trying looking up a manga forum. Most Manga artists or the more serious ones will know a lot of japanese

I don't know any unforntunately, and the Japanese is one idea, I could use Chinese or Mandarin, whichever sounds the harshest.

kozu - my ex is japanese and thats what he told me ... :)

Any idea on meanings?

I tried a fewtranslation programs, and got nothing, it's like the word doesn't exist.