well child marriages are permissible in Islam as we have the Example of Hazrat Ayesha(RA)'s marriage with Prophet Hazrat Muhammad(SAW) but at that time these marriages were not forced ones, but on the other hand, today these are enforced on boys and girls. thats the main problem.
but still after the results we can say that child marriages must not be done its better that marriages should be done at the time of maturity of both the sexes.
:)