What are the effects of second hand smoke to kids?

Actually, those who are called second hand smokers are more at risk of several diseases than those who actually smoke. Specially for children, specially if they have weak immune system. Problems can be related to the lungs and there are a lot of those. Since its your dad who smokes, you can explain to him that he can smoke but not near your son and try to explain the effects. Just a simple "my son will carry the negative effects of what hes doing" is enough for him to may understand what you are trying to say. I know that feeling because my dad is also a chain smoker.

OH, that's bad. It can lead to ear infections, early onset asthma, increase chances of allergies, and actually increase the chances of cancer for later in life. It does bad things. I personally am a smoker and i do have a four year old. But we don't smoke in the house, we don't smoke in the car. And if we go out to eat, we go to non smoking restaurants. So, just because there's a smoker in the family, there's no reason you shouldn't be able to ask him to step outside.