I was thinking of a steampunk music player using floppy disks: store a 32-bit (4 billion songs should be enough right?) ID onto a floppy, and have a player (it can be a Raspberry Pi with a USB floppy drive) read the ID, lookup the MP3 the ID corresponds to and play the MP3 from an attached storage device.

Because floppies get bad sectors, the ID should be stored repeatedly on it, 4 bytes repeated to fill 1.38 MB should be redundant enough!

I suppose without ID's, one can also store the artist name and song title, and do some text search to find the MP3. Or a YouTube video.

I was thinking child friendly, so using NFC tags isn't such a bad idea - plus I have a few hundred spare ones in nice plastic casings. I'd also just store IDs on them, and either have the media files preloaded (as seems to be the case here), or have it download it from my media server on first use.

Other thing I want (which they don't do) is the ability of resuming playback at the same position, even when putting it into a different player - that's one reason I still have some audio cassettes for the kids. No other medium I'm aware of does that kind of easy state saving. My idea there is to have the tags locked in the player in a way that gives me enough time to write the position if the user tries to remove it.

I did this for my child and it worked well. Arduino compatible RFID module, ESP32 with and SD card and I2S. I ended up renaming the MP3s to match the card serial numbers, rather than program each one.

There is a company / device called Yoto that is essentially this:

https://us.yotoplay.com

There have been multiple devices. I have been looking into the jooki box as well, which is quite hackable, tonibox is nice hardware (with already good firmware replacement), yoto is weird.

There's also yotoplay.com, although that one does seem to require wi-fi and cloud thingies.

Google tonuino. There are readymade pcbs you can buy for it