Pollisynth is a new iPhone app that will generate synth patches based on pictures you take with your camera, or import via the Camera Roll. It will analyze the image and assign waveforms to its two oscillators and LFO. Alright... this is gimmicky as fuck, but it is free and I think there is some educational value here. Want your kids to get into synths? Send them running around the house taking pictures of crap and playing with the results!
I was playing with it this morning, so it is kind of amusing for kids of all ages. Without any filtering or even pitch/mod wheels though, it will quickly bore experienced users.