Kid's Room Hideaway
No burglar worth his salt looks in a kid's room for valuables. It's just full of useless junk. So find somewhere in there where the kid won't find it either.
Between almost every pair of upper cabinets, there's a 1/2-in. gap. Take advantage of that gap by hanging a manila envelope containing, oh, I don't know, about two grand in hundred-dollar bills? Hang the cash with binder clips that are too wide to fall through the crack.
Slip a Box Inside a Box
Store a container of valuables inside a larger bin full of unappealing stuff. Label it accordingly.