I don't think it's gonna be drastically different either way but I'm personally biased towards smaller cities away from the coasts. In blue or blueish states but not complete democrat hegemonies. Seems like growing up where everyone is a democrat (at least in name) sets up an arc for people to react against that by becoming a republican, but growing up where most people are democrats (in the cities), but frothing conservatives are a bit more close to home, and don't provide an alluring counter as much because there are nearby counties, etc where they hold power, is probably helpful. Then, if you're paying attention, you realize how spineless the dem leaders are and how much worse than their own voters they are, and you're on your way to being a leftist.

But again I have nothing to back this up, its probably all a pattern my brain invented based on my limited life experience.

I don't think anywhere is going to have much better state mandated curriculum than CA but I guess in a reactionary area your school board could go bad real fast... places like chicago, minneapolis/st paul, pittsburgh/philly, all probably are decent choices but I don't think there's anything really that makes them better places to raise leftist kids exactly, so much as just to raise kids in a more livable urban environment where they might be able to have some freedom that doesn't involve a car. urbanism isn't everything but I can't imagine raising a leftist in deep suburbia except out of necessity.