Maybe its because pollution is more prevalent in big cities.
And maybe its a co-incidence that ultra-liberal, hover parenting psychobabble-infused mothers are more likely to live in big cities.
And maybe its a co-incidence that in big cities there are more psychologists telling them that its not their wishy-washy parenting that has resulted in uncontrollable brats. Its "the ADHD"... its the demons living inside their kids' heads, whispering in their ears, soaking up the ritalin.
And maybe its a co-incidence that big cities are more likely to carry left wing media that asserts that a smack on the hand for your kid, is tantamount to child abuse.