i have read somewhere that nikah can take place before puberty but not consumated and as soon the person hits puberty they have the right to proceed with the nikah or opt for divorce?
yes, that is correct. Again, if he/she reached puberty doesn't mean that he/she is able for sexual intercourse. Hence, it is delayed till he/she is able for it. This ruling is not only applied to young male/female, but also grown up male/female.
^because you appear to be knowledgeable can i ask something? If a trend is setting where elders are using the premission of child marriages to abuse the rights of children would it be alright to put a ban on it for a while? like i read soemwhere during famine Hazrat Umer r.a banned the penalty for theft (losing a hand).
akhee, not trying to be modest but I'm not knowledgable; a layman like yourself. As far your question, Allahu A'lam, really! We know that if a permissible act opens door to fitnah/sin and it causes more harm than good, then mujtahid scholars can issue fatwa to make it not permissible. However, such laws would only be possible to be applied if the country is somewhat ruled by shari'ah. And I have not heard about this particular action of Umar (radiAllahu anho), but I do know that for some other rulings he made his ijtihad to aviod greater fitnah and encorported them in shari'ah court of his time.
We know that this is not commonly practiced in our day of age for various reasons. In some areas (Muslim countries) where it happens, they are hardly following shari'ah and its limits. The scholars have stated that such marriages should only be done when the benefit outwiegh the risk by long shot. For example, the marriage of Prophet (sal-allahu 'alayhi wa salam): there was great hikmah (wisdom) and fathyl (benefit) in his marriage with Aishah (radiAllahu anha). Hence, we follow his (sal-allahu 'alayhi salam) sunnah.
Allahu A'lam