This is a noise maker which generates square waves, then mixes them together to make different sounds. You change the sounds by waving your hands over it. It's a simple circuit and it's noisy, so it could be useful for children to try electronics.
The circuit uses a "Quad Schmitt Trigger NAND gate" to provide 4 oscillators. These oscillators will either make a sound, or turn another gate on and off by connecting its output to another gate's input.
It's loosely based on a circuit in the book "Handmade Electronic Circuits" by Nicolas Collins.Video: here
The four oscillators are in groups of two.
The first in each pair makes a slow square wave which turns the second oscillator on and off. This goes into one of the inputs on the second gate. Because both inputs must be high for the gate to switch on, this connection will stop the second gate from working. The second gate oscillates fast enough to make a tone.
Finally the two pairs are mixed using the diodes to make the final sound.
Have a look online for more about how Schmitt trigger oscillators work.
It's probably best to have many different capacitors, so you can experiment with different sounds.
For an amplifier, I used an LM386 board from eBay.