Over the past couple of years it seems that people have confused these two words.
Here is an example:
www.bbc.com/news/uk-scotland-glasgow-west-39514028
"every effort is made to avoid your baby being sick" when winding children.
To my mind, "to avoid" means to go out of the way of something that is there. "To prevent" is to stop it happening in the first place.
So in the example above, parents should duck out of the way of their baby's sick, where I'm sure they mean that you should try and prevent it happening in the first place. (Though how you are supposed to do that is a mystery to me, but we are talking semantics, not biology, here)
One online dictionary definition of "avoid" is
>>keep away from, stay away from, steer clear of, give a wide berth to, fight shy of<<
All of which make quite clear that it is about going out of the way of something you can't change or remove, but which you don't have to get involved in.
To "prevent" an argument/war/fight is completely different from "avoiding" one. If you "prevent" the a/w/f you stop it happening. If you "avert" it, you re-direct it into other channels (discussion, treaty). If you "avoid" it, you don't stop it happening, but you keep away from it.
While I try and suppress pedantic thoughts, as I do accept that language evolves and progresses, I do have a problem with more and more words being used wrongly. If words are simply allowed to mean what the speaker thinks they do, then we will soon not be able to communicate with each other at all, and misunderstandings will abound.
All they say is 'Well, you know what I mean'. Teachers can be the worst offenders for this, so don't look to schools to change children's language use.