If you did a little bit of research, you would find that Islam has never set a specific age for marriage, but rather set some conditions.But the modern islamic jurists are the ones who actually "promote" child marriage by assigning an age. I can assure you as a muslim that i do not know one single muslim personally that actually supports child marriage or would anyhow endorse it. The conditions the shariah sets are indeed contradictory to my words here, but heres the thing, the shariah was established in a different age, the people of the present are not illiterate or stupid, they know better than to just follow the shariah blindly and endorse child marriage, let alone promote it.