There's lots of evidence that second hand smoke causes respiratory illnesses in children, so given that the levels are high, then you'd expect (parents) are exposing their children to health risks.

大量证据显示，吸二手烟可导致儿童的呼吸系统疾病，比例之高，你可以想象得到，家长正在使他们的孩子的健康暴露于危险之中。

youdao

In recent years, medical evidence has pointed to the harmful physical effects of second-hand smoke.

VOA: standard.2010.06.15

Although there is some evidence that artery damage caused by second-hand smoke in adults may be reversible, LaVan says it's unclear whether that's also true for adolescents.

VOA: standard.2010.03.04

Despite the bally-hoo over second-hand smoke, there is no good evidence that it poses a measurable risk to bystanders.

ECONOMIST: Land of the smoke-free

There is plenty of evidence that "second-hand" smoke - breathed when you are in the same room as someone smoking - can be harmful, particularly to children, and some parents adopt a strategy of never smoking in their child's presence.

BBC: Warning over 'third-hand smoke'

Martin Dockrell, director of research and policy at the campaign group Action on Smoking and Health (Ash), acknowledges that there is no clear evidence of a significant harm to health from second-hand outdoor tobacco smoke.

BBC: New York's outdoor smoking ban: Will the world follow?