https://alex.miller.garden/sonic-circuit/ A weird and cumbersome web based synthesizer. In the examples below, double click on a node to trigger a signal in the circuit and produce sound. Here is a "song" that a friend made with it: https://alex.miller.garden/sonic-circuit/?2.9.C4.m.1.15,6.9.... And here is "Happy Birthday": https://alex.miller.garden/sonic-circuit/?3.1.G3.m.1.24,4.1....
It would be a nice tool for kids on tablets if you added touch input. Maybe tap to pop up a menu with all the options.