If you are talking about cultural child marriages - it really does not seem these children want to get married young. Even in the cases where the children were of the same age.
From the mouths of these:
While child brides in Rajasthan tend to be married off very young, it is usually to grooms of a similar age and it is not until they are older, about 15 or 16, that they actually start living together as man and wife.
Even so, being married so young does limit their opportunities.
Rukhmani, a 26-year-old mother of two, was married at six years old and started living with her husband when she was 15. "Had I been married later, I'd have learned to read and write," she says. "If I'd studied, I wouldn't have had to work in the scorching heat, harvesting in the fields."
Mamta, another child bride, also regretted not being able to study, which she felt would have given her a chance to be independent. Instead, she'd felt she had no option but to endure regular beatings from her husband.
Bangladesh has the highest rate of child marriage in South Asia and the fourth highest in the world, despite child marriage being illegal here, too. In Bangladesh, young girls are married off soon after reaching puberty and usually move in with their husbands straight away.
Seema, aged 14, married and moved in with her 19-year-old husband a year ago. Her life now is radically different to her carefree childhood.
After marriage, what is my work now? Washing dishes, cleaning the floor, washing clothes and cooking," she said.
Seema is now four months pregnant and overwhelmed. "Before I was a kid, and now I'm having a kid. Of course it's scary."
They don't sound too happy nor do they seem like this was their choice. But it is acceptable under their culture.
https://www.bbc.com/news/magazine-15082550