As decided by Little Man:
Vacuum hose extensions
He never tires of snatching them from the closet when I'm not looking. (and have forgotten to lock said closet) Whacking walls, couches, and sometimes sisters, is always appealing to Little Man. There's also the added benefit of using the tubes to extend his reach to anything up high or on counters.
There are some things that may be better locked in a safe... apparently vacuum hose extensions are one of them.