I'm not against child marriages, actually in ideal situations I might agree with it, I think it's not bad thing when people marry at 15... Even romantic. (Many people will disagree with me on this)

But child marriages as you described them is a bad case even for someone me...

These marriages result from a web of factors including poverty, lack of access to education, child labor, social pressures, and harmful practices.

The cases where I think child marriage is okay, when those children are strong and can take responsibility (many adults these days can't but that doesn't have to do with age)... The man must be fair and soft with the woman, and they shouldn't marry her to someone who'd beat her. Because it seems that most of the problem is there:

Thr girls who are married at small age are likely to be the victims of domestic voilence as conpared to the womens who marry later.

That and it must be done with their agreement and not under pressure.

I think this practice is spread in Islamic places that understood the Islam teachings wrong, women aren't less valued than men in Islam and while it allows younger marriages, it comes with a very strict rules to make it succeed.