Storage of toys??

Ok so me and my boyfriend have a collection of toys and stuff for the bedroom now. We are dom/sub couple in the bedroom and some of our collection is large and some small. We were storing stuff in random places since we live alone and that was fine. However I have a niece who is due in November and I know as she gets older will be curious so we’ve recently decided to get storage with a lock on it that we can put in the bedroom for easy access.

I was thinking of just getting a travel trunk and using that since we can easily buy a padlock for it. However we’ve started having trouble with our master bathroom tub and my brother and Dad who are fix it themselves men come over to help my boyfriend work on it and my sister in law and I sit around and watch tv and help out if needed.

My question is how do I explain what is inside a padlocked trunk when they ask? I need something to say because I know good and well my sister in law will ask simply because she’s a curious mind. I know she doesn’t mean to be intrusive or rude she’s honestly just curious and has no filter lol. No harm done I just need something not suspicious as an answer because if my parents found out I had this sort of relationship with my boyfriend all hell would break loose. Thanks y’all!