I saw in one of your posts in this thread that your kid liked legos and minecraft. I suggest the LittleBits synth kit. It is made up of little building blocks that basically make up a synthesizer. You can put them together in a bunch of different ways to make entirely different musical instruments. If they like warping their voice, I bet they would like warping circuits to make cool noises. It also teaches great engineering skills like breaking down big things into smaller ones as well as wonderful creativity exercises, like making cool fucking noises. They come with some starter build instructions, too. Just like legos.