This is super useful to know about!
The sprite designer & waveform editor / tracker is a really good creative introduction to computers for small children. And you can jump straight in to doing this with the above web link.
(For those new to Pico-8, hit 'esc' from the Lua console to bring up the editor tools, then click on the icon in the top right.)
(For those new to Pico-8, hit 'esc' from the Lua console to bring up the editor tools, then click on the icon in the top right.)