Brandy,
I've noticed the trend as well....
As an adoptee, born in the early 70s, I grew up with the stereotype that all birthmothers were young teenage girls who had "gotten themselves in trouble". Once I found my birthmother, I was very shocked to find out that she was a 40 year old business woman when she had me and was a single mother with a 6 year old daughter!
As to how the new stereotype has come about, I really don't know.... but it is very sad.
We adopted our son from a domestic newborn adoption, and both of these stereotypes couldn't be further from the truth!!
So how can we change it? Education, correcting people, talking about it..... Every single time we see a single stereotype or assumption, about anything (I have been assaulted with a lot of stereotypes in my life), we need to stand up and say,
NO! that is not correct!!