I'm a smoker too and wouldn't smoke around any of my younger cousins but the threat of force towards those that would is wrong. Also, the threat of second hand smoke has been debunked and this nanny statism is not something that we need more of.
You are right on the nanny state. But even if it was debunked smoking is not a good habit to "teach" for children.
Sometimes I think if the state don't want us to smoke then smoking must be a good thing
. (Actually nicotine is far better and safer anti depressant than anything what the big pharma can make.)