Here, we call them “safes”. :rolleyes:
Good Vibrations has a lockable box for such purposes. (I’d link directly to it, but I’m at work now.)
If you’re willing to go industrial, Pelican and Anvil are the ways to go.
Pelican has a great warranty, but is your child under five?
Footlocker. Army surplus store.
Could be painted or textile covered to suit your decorating taste.
Or try an ammo box. Sporting goods, army surplus, or a farm supply store should have them.