Calling teenagers "children" has real effects. The UK is considering a law to prohibit marriage of anyone under 18, and this is presented as "saving people from child marriage."

The stated reason for this law is to prevent the practice of compelling someone to marry. Doing that is clearly an injustice, but I don't see that it becomes any less wrong if the victim is over 18.

Maybe it is unwise for people under 18 to marry. Maybe it is unwise for people under 21 to marry. Or under 31. I clearly don't know, but it is not about being "children."