My question involves criminal law for the state of: California

1) Is it legal in California that a parent serves alcohol to his 18 years old son? And, if the 18 years old drinks on his own without parent's permission, is he violating any laws? And, if that 18 invites friends to his house and they all drink (without parents home), are they all violating laws? Any?

2) If a 16 years old girl went to her friends house and got hold of a bottle of vodka and they all drank in a park but she got drunk (all others were taking 1 or 2 sips). Who are responsible for her intoxication? The parent who didn't lock their vodka? Or, the girl's parents who didn't supervise their daughter? (She lied where she was bout).

I need to ask the above questions so I can be of a help to those parents who think it is ok to provide alcohol to their children before it is too late. As for the minor drinking, I believe that girl has bigger problem than alcohol drinking... sigh!