hey hold your horses. heres a few things to know:
the age system varies country to country. eg, in uk anyone under 18 is still not legally noticed as an adult
in Islam, an adult is someone who is baligh aka past the stage of puberty
majority of kids in warmer climates reach their puberty earlier than those in colder climates
so.. what age range do you mean when you say 'child'?
I dont know what you are trying to imply but child marriage is child marriage, no ifs or buts. Just because a girl just underwent puberty doesnt mean she needs to get married, weather its warm or cold. Such marriages are nothing but pedophilia in this day and age.