Relevant laws are as follows (click cite titles for links to official law):
Article 17, Section 1292 of SF Municipal Code
It is illegal to loiter while carrying a weapon. In this statute, weapons include knives with blades over 3" and spring type knives (see next part below for these) and many other implements of destruction. Note that CA law does not have a length limit, and this length limit
technically only applies if you are loitering (a wobbly subject by itself).
Article 17, Section 1292
No switchblades at all, period. This goes beyond CA law which normally allows for switchblades under 2" in length. Furthermore the law bans "any knife any blade of which is automatically released by a spring mechanism or other mechanical device." This would seem, in my non-CA local, non-lawyer opinion, to also ban assisted openers.
Article 17, Section 1293
Summary - You cannot give or sell ANY knife to a minor unless you are their parent or guardian. Note that there is nothing against
possession though.
Article 4, Section 4.01
You cannot carry various weapons on park property without permission, no matter whether they are concealed or not. This includes fixed blades ("Dirks" and "bowies") but not folders, which seem to be ok.
Naturally, you are subject to normal CA law as well:
Fixed blades have to be carried openly and not in places that freak people out. Folders of any length are allowed to be carried concealed provided they are not autos or balisongs (normally outside SF, these can be under 2" and still be legal)
Just one clarification on pocket-clips in general: Pocket-clip showing can be consider concealed or open depending on which gives the cop an excuse. In LA, open carry of folders over 3" is the crime, so pocket-clip showing is Open Carry and illegal. In other areas where concealed is a crime, pocket-clip showing is considered concealed.