[qiqitori]

Here's a well-known one that is actually a full-blown circuit simulator:

https://www.falstad.com/circuit/circuitjs.html

If you go to e.g. Circuits -> Combinatorial Logic -> Full adder, you can see that digital logic is available too. (Uses a lot of CPU, so maybe reduce simulation speed and current speed. You don't need those for digital stuff.)

Maybe it doesn't look flashy enough for kids though :p