Smoking has been proved to be harmful and so rules have been made to protect children from second-hand smoke. Vaping hasn't been around long enough to know the damage it could cause so until more research has been done it should have the same restrictions.
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There are far too many children/teenagers thinking that vaping is safe and so try it for themselves. Vaping can still contain nicotine and so they are becoming addicted to it. An addiction to anything is dangerous. There are restrictions for smoking in cars with children or non smokers being in the same car and as vaping hasn't been proved to be safe I don't think children should be exposed to vapor in a confined space either.