Unhealthy air is making a comeback in the Keystone state, driven by a warming planet and wildfires raging far away.By Marie CusickKaren Schaeffer is used to spending a lot of time thinking about how to keep kids happy and healthy. But only recently has she confronted a new problem at the childcare center she runs in Lititz, Pennsylvania: hazardous air wafting south from wildfires blazing far away in Canada.