If your children are going to try pot then the law will not be what stops them, as this is no longer seen as a great deterant for using the drug (espicially to teens)
Instead educate them about the long term effects that pot smoking has on the mind eg. short term memory loss, and the de-motivating factors of the drug. You then have to trust their better judgment and common sense on this matter and not the countries laws to protect them from this drug.