Yeah, so here's the thing...you can't. So, mind your own damn business.
Dear Prudence,
My husband, our infant daughter, and I recently bought a house in a neighborhood near where I grew up. For the most part it’s a really lovely, artsy, up-and-coming area. We’ve met our direct neighbors on both sides, and everyone’s been super nice. The issue is with our new neighbors across the street. Their house is the eyesore of the neighborhood—overgrown bushes and trees, broken-down cars parked along the street, etc. Most of that I can brush off, but what I can’t seem to let go of is that I see them smoking cigarettes in front of their two elementary school–age daughters. Smoking around children is so detrimental to their health. Personally, I am allergic to cigarette smoke and very sensitive to it. Also, my grandmother smoked until it killed her, and my mother and all of her siblings have lifelong respiratory issues due to their exposure. I can’t imagine there’s any tactful way to ask these people to stop smoking in front of their kids, but perhaps you have a suggestion?
—Smoking Neighbors
Re: Yeah, so here's the thing...you can't. So, mind your own damn business.
And you're going to have to let go of the appearances in your "up and coming" (read: most likely a mix of a variety of socioeconomic backgrounds and YOU are coming off as someone of privilege who is really judging those who appear to be less well off).
If it's not coming into the house, find something else to do.
As to the smoking - I can't think of any way you can bring it up without looking like a condensing jerk.
That's about it.
If you're speaking to neighbours, you could mention the allergy that you have - but that's all you can do.
Even a simple "hey, I know it doesn't often happen but could you be careful on the blowing smoke? I have an allergy"
Karen just sounds sanctimonious AF and needs to mind her own business...prerferably while guzzling her gallon of mom box wine. This reeks of white gentrification to me.
"We moved into an area that still has some of the originals living there and we know that this neighborhood is on the upswing. We're still stuck with some of the old ones that don't know how to properly landscape and who park their old cars in the front lawn because they're probably working multiple jobs around the clock and can't afford to buy the new Q7 that I'm leasing. Aaaaaaand they do this perfectly legal thing of smoking in their yard. We know it's bad right? They must not. I'm going to tell them and the new neighbors will thank me."
It's liberal NIMBYism. "I want to help and put money into areas that need it but PLEASE keep that stuff out of my living room window."
Unless they're blowing smoke AT her she needs to sit back down.