I understand this may be the biggest negative of the new law, and could potentially leave parents vulnerable to prosecution by offering a restricted substance to people under 21 years old.
Answer - I'm a medical marijuana attorney with Scot Candell and Associates, Attorneys at Law
Proposition 64 legalizes the possession of cannabis for adults over 21. It also changes the penalty or all cannabis offenses, so that someone between 18-21 will get a fine for being in possession of cannabis, and a child under 18 in possession of cannabis will be required to take classes on the harmful effects of cannabis on children. I am unaware of it changing the law related to parents.