I just made my own pretty stealthy box. It took about a month and around $1500 (lumber, paint, stain, brushes, countersink bits, light, fan, blah blah BLAH). I figured it'd cost about a grand, but there's always things you forget and they add up.
Anyway, link to the details and a few pics is here:
I dunno if it'd fool children, but it's crammed into a corner, and the fan isn't really all that noticeable if there's any other sound in the room. At least it looks reasonably stealthy, and if I'm gonna have someone in this room, I'd just turn off the fan, and throw a shirt or two on it to add to the realism. I'm not sure anything other than a securely locked door is REALLY kidproof. I mean, when I was a kid, I got into pretty much everything, sometimes even the stuff that WAS locked. Heh.
I considered a fridge too, but decided that it'd just be too much hassle to work with, compared to wood. I could be totally wrong about that, of course, since I've never tried to modify a fridge, just the feeling I had that wood would be easier.
"Before you consider one an enemy, first walk a mile in his shoes. Then, if he *is* an enemy, you're a mile ahead, and you have his shoes."