I've build a couple of similar boxes for kids. The more complex and unpredictable they are, the more fun they are.
Just use any old switch you can find. Rotary, SPDT, 4PDT, push buttons, anything !
Buzzers, motors, vibrators, LED's, LDR's.
You can add more complex circuits. One switch I had did nothing, but it was wired to a capacitance circuit. So if somebody put their hand near it, it would turn everything off momentarily. The kids though the "secret switch" was the most fun, and they would spend hours trying to work out what that switch did, but every time they tried to change it, everything went off before they could even touch it.
A friend built this one many years ago.
http://home-and-garden.webshots.com/photo/2379743640048941318GTgarM
He didn't build it for children, though he was a big kid.
It was originally a guitar amplifier. I made a passing comment that it was a bit of a dull looking thing, so to spite me he decided to make it "better".
It has an audio amplifier and an AM and FM radio built into it as well as a microphone and line in inputs.
It has some (many) surround sound delay lines in it and each of these can be switched, mixed, and fed back on each other.
Their delays are variable and there are several oscillators, mixers and other weird audio circuits one would only expect to find in RF circuits.
The sounds this machine can produce are even extraordinary for a Dr Who soundtrack.
One of my favourites is the simplest. A variable delay line is varied with a 0.2Hz sine wave.
Put the radio on to a new reader and they start to talk real fast before they slow down and speak slowly and then start talking fast again.
Rather than using a sine wave, a square wave can be used and the effect is sudden rather than gradual. The amplitude of the bias oscillator controls how fast or how slow the delay line works.
It doesn't take long to realise that even with only a couple of variables, the number of switches and controls can be very large.