I'm not actually a parent yet, but I do plan to have kids and to raise them in a mixed-income neighborhood (somewhere in Cambridge MA).

I do think peer effects exist. Having worked in a local school full of both "underclass" kids and professors' children, which is the mix you get in Cambridge, I do think the poorer kids have a somewhat negative effect on the richer kids. I expect there will be some negative effects to my kids from not living in a bubble. However, I love the area and I think that living there will be good for the family, better than going into the kind of debt Vladimir_M mentioned to afford all-rich neighborhoods or private schools. We like living in a city, we like not owning a car, we having no debt. Those things mean living near some poor people.