We will go hypotheticals here as to be the best of my knowledge, and greatest of hopes, I am not a father and never will be. That and I am also a terminally boring bastard that does not even do caffeine as a general concept (though that is more because coffee and tea are both disgusting and despite my advanced age I can wake up, throw some clothes on and walk out the door 30 seconds later fresh as a daisy).
Anyway the question is manyfold
Am I worried about my kids taking my drugs to use for themselves (buy your own and all that)?
Am I worried about my kids taking my drugs thinking they are sweeties and tripping balls (or even badly dosing owing to size differences and metabolism differences) as a result?
Am I worried about my kids finding out I do drugs for whatever reason (divorce case, the police also doubling as the fun police, general "do as I say, not as a I do").
Each of those pose different security scenarios, and will vary with the drugs you take -- weed has a rather distinctive smell that believe me sticks almost as bad as tobacco and is probably more noticeable while it is still active. This goes double if you go in for skunk or, worse still, something like soapbar (don't do soapbar). If you microdose on LSD, psilocybin or something you take orally. Other smokables can be worse still, though fortunately most people don't know the smell of meth or crack.
It also depends on you as well -- if you are a coke fiend then despite it generally being snorted then at the same time I have never met one that does rails off a small mirror that does not have said same mirror be coated in remnants. Also never met anybody that had long term coke use be a positive effect on their lives so maybe find something better there. It is the equivalent of hiding your porn behind 7 proxies, a locked door and then in a post spurt bliss only minimise the window.
Back to the first two scenarios then these are very different threat protocols.
For the first you generally find them to be older kids that are sophisticated, and in the general threat assessment also present and keenly aware internal threats that you can't simply dispatch.
For instance if I tool up and raid your house in a 30 minute smash and grab I might not look in a door frame or vent cover. If however said kid is in bed at night and hears you fiddling with such a thing, possibly several times on the trot, and then has that nice sweet smell waft in (one they will know -- depending upon where you are in the world most kids above about 13 will have some idea, and 13 is high in some places) then yeah.
For the former then up high and locked with a key that can't be easily found or picked. Distance can also be a thing -- might be nice to skin up in the comfort of your room but if you have to walk somewhere a bit further away to find it there (or maybe with a friend) then that is a different matter again.
Decoys are good. Hiding a bit of harmless porn, some lube,
a dilly or some condoms to spare them finding your stash is one thing, though that might mean having to go procure some dead tree porn which can be hard to do (I have no idea where you would get anything of merit these days) and also potentially admitting to your kids that you don't know this computer lark (the other alternative of printing your own casting you as even more of a luddite). While you appear to be American you also say California which means anything more shooty than a gat gun will probably see a swat team kick down your door which reduces another possibility of a decoy there -- for safety you can also get something that nobody stocks bullets of a suitable calibre for).
Kids also grow up fast, and if they have elder siblings they can gain a skills buff from their other party members (which can include outside temporary members), so you also want to consider that. To that end be sure to continually evaluate your measures, or seriously overdesign from the start (and then still evaluate things on a reasonably regular basis).
