No, not exactly. Yes, their health is damaged, they lose years of life expectancy and are at increased risk for early onset of diseases.
Not good. But consider, for example, that dense urban environments subject people to the same thing. Are they banned? Do we take cities and industry away? Heck, we built industry on broken backs and blackened lungs - not least of all children's.
Yep, we're better now, but honestly not by much. So, let's get back down to human terms.
A child is growing up in a reasonably loving home; one or both parents happens to be a smoker who's lax on doors and rooms and such seeming trivialities.
They have a good environment; ethical parents who teach ethics, support their education, etc., and they have, for all purposes, a positive life trajectory ahead of them - which, aside from the emotional and intellectual environent created by their family, is also greatly reinforced by say, lower-middle class or even working class economic basis; the family owns some assets, earn a decent living, and can afford to shape society's advantages around their child to a degree.
This is an immeasurably better point from which to live one's life than getting hauled out of your home and the only family you know because your parents are inconsiderate smokers, and packed off to a foster home where, if you're lucky enough to avoid outright physical, sexual and emotional abuse, is still going to be, in almost all cases, emotionally sterile, and unloving, with minimal "parental investment" in your life and future, and almost nothing in terms of economic support.
If it's in legal terms, the limits of enforcement need to be very clearly defined. I would support, for example, it being illegal to smoke in the same room as your child, with violation of this law translating to mandatory counseling, with rehab at most upon repeat offense, stay-at-home rehab for single parents.
