Comment by sandreas
There are several projects here in germany doing similar things.
There is https://tonies.com, which is cloud based and pretty expensive, but hackable (https://github.com/toniebox-reverse-engineering/teddycloud).
Then there is the RFID Jukebox: https://github.com/MiczFlor/RPi-Jukebox-RFID
And Tonuino: https://github.com/tonuino/TonUINO-TNG
I built ours with the RFID Jukebox and wrote a little tool called labelmaker to print labels for audio books and music: https://pilabor.com/projects/labelmaker/, but in the end it took too much time to print so many labels :-)
I recently bought the toniebox to hack it for my son's 4th birthday. It has become his favorite object.
I considered building sometime custom, but the tonie hardware is cute, portable, and lovable in a way that would be hard to replicate.
It has been really fun for my wife and I to listen to our favorite music in the car, and then when my son says "I like this song" I "burn" him a little disk that evening.
He's turned into a little DJ, and has memorized a handful of his songs (and dances and sings along).
One caveat is that finding compatible NFC tags is a little bit complicated. if you buy from RFIDfriend [0] then they take a couple weeks to arrive from Germany.
Highly recommend!
[0] http://RFIDfriend.com