Children like to imitate adults.
To a child, being a grownup is a very desirable thing. We might be surprised to find out just how grownup they feel when we ask them to get us a beer from the refrigerator or an ashtray from the cupboard. A child can understand and accept that there are differences between what adults may do legally and what is appropriate and legal for children. We want to continue to reinforce this understanding by not abusing legal substances or using illegal drugs. Most kids are already pushed hard to act like grownups.