What are you going to do, send police inside people's private homes to make sure they aren't smoking in front of their kids? Come on, you can't enforce a ban like this without infringing on people's rights to privacy. Plus you always have at least one crazed liberal that wouldn't want the parent to even be on the same property smoking while their kid is nearby.

I'd say child obesity is far more of a problem endangering many more kids than parents smoking tobacco/pot. I'm not saying that's good to do, but just that it's not as prevalent as over-feeding their kids. You can't expect big-government to solve these issues, it all comes down to quality parenting which cannot possibly be monitored by government.