My take
This would be my priority of thoughts:
1) Son's future interests;
2) Your visitation interests;
3) Your wife's interest in 1/2 of weapons or accessories you purchased with earnings during marriage. (you live in CA, a community property state, so she owns half and can force a sale of such guns if she wishes to (i.e. if she is smart--or gets a smart nazi family lawyer to advise her to say she wants to go shooting and own 'weapons' or that the value of the items is elusive or "indeterminative" and should be sold to better determine and allow for division of their value)). This would, of course, depend on the judge (i.e. accepting her argument), but judging from the cases I've read in law school and my peers, the climate in the legal community is like 10 to 1 leftist. (Even Bush's head lawyer in Florida was a Democrat.)
Advice: kiss her ass and be sensitive on the gun thing until she's booted. Just approach it as a promise to yourself and him to give him an opportunity in the future to learn the ropes when he can take it to heart. The law recognizes 7 as an age where children begin to gain some legal mental capacity, followed my near adult mental capacity at age 12. Looking at those as a guage (albeit an arbitrary one), I would say you don't push her at all on introducing him to weps (even toy ones) until after age 7. Besides, he'll discover them on his own.
Unfortunately by the time he's 18 all we'll have is grandfathered 870s anyway, and those will have to be stored in a 'central' range location, to be accessed only at designated times. So he'll probably have to go into the military to get any legal rifle training anyway.
(P.S. I'm married 3 1/2 and my wife is damn stubborn so I do appreciate how hard it is to kiss a bitch's ass--albeit the condition is temporary in my wife's case.)
Bitches, man, Bitches,
MC