I know exactly what you mean Melissa! I've gained 80 lbs over the past 5 years (I need to lose 110) and I have noticed the same thing. Even most of my guy friends who used to "flirt harmlessly" no longer do that! It is painful and I'm glad I'm going to do something about it.
Unfortunately, "it is what it is" and I don't think we can change people who already are like this. It makes me feel differently about the guy friends I do who treat me this way even though they don't realize they are doing this.
Hopefully your boys will influence their peers.
Good luck!!